How to handle dummy's revoke due to a hidden card?

Question: A final bid of 3 spades is made. The opponent leads a club and dummy lays down a hand showing no diamonds. Declarer wins the lead trick in hand and leads a diamond  trumping it in dummy. Declarer then returns to hand and leads a second diamond trumping again. He then plays a club from dummy and in moving it reveals a hidden diamond. Since there is no penalty if declarer revokes, how is this managed?
Comment: @Jyrki It is also not correct that there is no penalty for revokes by dummy. There is no automatic trick penalty, but the directort will restore equity under law 64 C. See my answewr.
Comment: Presumably you meant that *there is no penalty if* **the dummy** revokes.* The declarer can certainly revoke, and the usual penalties apply.
Comment: And see https://www.bridgebase.com/forums/topic/48231-hidden-card-in-dummy/#entry577198
Answer: I am not a TD, but I am a qualified Club Director, and this situation is actually a fairly clear one. Under the Laws of Duplicate Bridge , laws 61-64 govern revokes. It is a common misunderstanding that there is no penalty if the dummy revokes. There is no automatic adjustment in such cases, but the Director should attempt to restore equity, and a proper rectification should be made.
I quote only the relevant sections of the laws below, for reasons of space. Please see the full laws linked above (2017 version).
Law 61 A defines revokes:

Failure to follow suit in accordance with Law 44 or failure to lead or play, when able, a card or suit required by law or specified by an opponent when exercising an option in rectification of an irregularity, constitutes a revoke.

The situation described is indeed a revoke.
Law 63 A provides:

A revoke becomes established:

when the offender or his partner leads or plays to the following trick (any such play, legal or illegal, establishes the revoke).
when the offender or his partner names or otherwise designates a card to be played to the following trick.
when a member of the offending side makes a claim or concession of tricks.

The revoke described in the question has indeed become established.
Law 64 B provides:

There is no automatic trick adjustment following an established revoke (but see Law 64C) if: ...

the revoke was made in failing to play a penalty card or any card belonging to dummy.

Law 64 C provides:

When, after any established revoke, including those not subject to trick adjustment, the Director deems that the non-offending side is insufficiently compensated by this Law for the damage caused, he shall assign an adjusted score (emphasis added)

Such an ADJUSTED score would be appropriate and required in the case described.
Law 12 A provides:

On the application of a player within the period established under Law 92B or on his own initiative the Director may award an adjusted score when these Laws empower him to do so.

The Director may award an adjusted score in favor of a non-offending contestant when
he judges that these Laws do not prescribe a rectification for the particular type of
violation committed.
The Director awards an artificial adjusted score if no rectification can be made that will permit normal play of the board (see C2 below).
The Director may award an adjusted score if there has been an incorrect rectification of an irregularity.

Law 12 B provides:

The objective of score adjustment is to redress damage to a non-offending side and to take away any advantage gained by an offending side through its infraction. Damage exists
when, because of an infraction, an innocent side obtains a table result less favorable than would have been the expectation had the infraction not occurred.

Law 12 C1 provides:

(a) When after an irregularity the Director is empowered by these laws to adjust a score and is able to award an assigned adjusted score, he does so. Such a score replaces the score obtained in play.

(b) The Director in awarding an assigned adjusted score should seek to recover as
nearly as possible the probable outcome of the board had the infraction not occurred.

(c) An assigned adjusted score may be weighted to reflect the probabilities of
a number of potential results, but only outcomes that could have been achieved in
a legal manner may be included.

(d) If the possibilities are numerous or not obvious, the Director may award an artificial adjusted score (see C2 below).

and 12C2(a) says:

When owing to an irregularity no result can be obtained [see also C1(d)], the
Director awards an artificial adjusted score according to responsibility for the
irregularity: average minus (at most 40% of the available matchpoints in pairs) to a
contestant directly at fault, average (50% in pairs) to a contestant only partly at fault, and average plus (at least 60% in pairs) to a contestant in no way at fault.

The director could attempt to go back to trick 2 and determine what would have happened had the revoke not occurred. Presumably the declaring side would have then lost trick 2. But it may not be at all obvious what the defense would have led or how the declarer would have played on such a lead. If the declarer has the remaining winners such that they can be cashed no matter what the defense does, the director could simply transfer trick 2 to the defense. But if there is significant uncertainty about the result in such a case law 12 C (1) (d) would most likely be applied, and the director would assign an artificial adjusted score.
Both sides have a degree of responsibility for the dummy, but the declaring side has the primary responsibility. Specifically, under Law 41 D the dummy player is responsible for properly displaying the dummy's hand. I would, in such a case, assign the declaring side an average minus, but assign the defense an average, not an average plus. There is an argument for giving both sides average, and for giving the defense average plus, but I think the defense is at least "partly at fault" here. So that would be my ruling on the facts stated above, if the outcome with the diamond loser were not rather clear-cut.
Comment: @Jyrki Av+/Av- would be a reasonable decision. The old rule that all players are equally responsible for the dummy is long obsolete, but still often quoted.. Trying to determine what would have happened had the card been displayed properly, or found when the dummy was to play to trick 2 is hopeless without the full deal, and might be unwieldy even with it, unless declarer's other tricks are cold.
Comment: Thanks for the added details. It was unclear to me to what extent the defenders would be to blame. At matchpoints I would have expected an Av-/Av+ decision, but I also see your point. Unless we see the hand it is probably pointless to try and gauge what might have happened with the dummy properly displayed.
Answer: David Siegel has the laws almost perfect (and thank you for that!)  He didn't mention that there is also no automatic trick penalty for the second revoke in the same suit (even if it wasn't from dummy), 64B2: "it is a subsequent revoke in the same suit by the same player, the first revoke having been established."  But either 64B exception works for the second revoke here, so no matter.
But there are multiple infractions here, and we have to consider them all.  Like anything with rulings, some things depend on Regulating Authority regulations and guidance; I'll speak for the ACBL because that's where I direct.  Other RAs would have slightly different decisions:

When dummy put down a 12-carder, did that affect the defence?  In the ACBL, we protect the defence from misinformation from mislaid dummies (again, "everyone's responsible for dummy" never has been a law).  Doesn't look like it here, though, declarer is in control after trick 1.
When the first ruff occurred, were the defence damaged, or are they going to get that trick anyway?
When the second ruff occurred, were the defence damaged over where they would have been after applying the law to the first revoke?  It's possible - if they were able to take the second diamond, after the first ruff, they might have been able to pull enough trump that there was no second ruff, or take enough tricks that it wouldn't matter, or not set up the diamonds, or...

I disagree with the comment about Average plus/Average minus, however.  I'm a bit of a stickler for this; it's almost always a cheapout.  The quote is: "If the possibilities are numerous or not obvious".  I know this was a trick 2 thing, but the possibilities are rarely if ever numerous or not obvious in this situation - either they would have got the club and don't now, or they would have got the club and still will, or they'd be able to stop the second ruff somehow.  I have never, in over 20 years of directing at clubs and tournaments, needed to give a L12C1d ruling.  Sometimes the weighted score (L12C1c) has 4 different options, but you can do it. (And yes, awarding a weighted score in ACBLscor is incredibly difficult.  Other scoring programs handle it much better.  So I can see a club director who doesn't know how having trouble with that).
I don't like A+/A-, because what if just getting there was a 90% score, even if we give the defence everything they are possibly entitled to?  Giving out a 40% for a "minor missort" seems overharsh.  Also, what if they're in a hopeless contract, and even if equity is "score stands", the non-offending side is still booked for 80%?  Is it fair that the "minor missort" gains?
Comment: Ehh, you've never given A+/A- because something happened *at a point where you couldn't otherwise judge the result*?  For sure A+/A- isn't right if the play for 3S= is obvious, regardless of the diamond ruff, and equally it's terrible if (For example) 4S= is trivial and reached at most tables, or if 3S doesn't make without the 'bonus' transportation - but if most tables are at 3S, and it's 50/50 to make, and requires a clearly different line of play, what else can you do but award the A+/A-?  It's not fair to assume declarer will see the correct line of play, is it?
Comment: Anyway, I do think that the TD could also strive to give a quick evaluation of the situation (often leading to Av+/Av-) **as an initial call**. Then inform the players to appeal the decision later. Say, if this is a club evening. To reach a better decision the TD may need to consult a panel of trusted players. Those trusted players are most likely playing in the same event, and are unavailable at this instant. A TD pressed to post running scores will need to score the hand some way. Yes, there will be an asterisk in the running scores, but... Sorry about running away with this :-)
Comment: I have, of course - the traditional "East swaps the boards, three players take their hand out, North swaps the board because she's the Lord of the Table and it's Her Job, and nobody notices until dummy comes down", or "East opened 2D Multi in a pair game".  But I have never given an artificial score when a result had been obtained.  I have never used 12C1d.  I work very hard at that.  Now that the ACBL has gone for weighted scores instead of the 2007 12C1c, the ruling is harder to make and to score, but both fairer and easier to deliver.
Comment: For your example: First, if it's this example, declarer gets no relief from dummy's infraction.  He will try the ruff line, and whatever happens, happens (possibly weighted depending on defense options). But say that third hand won the first trick and returned a trump hoping to kill ruffs, and that picked up partner's trumps and let the contract through; if she saw the singleton diamond, the "stop ruffs" line is still possible but not clear, and the successful line is reasonable.  Now 12C1e gives me the ability to award say 75% of 3S-1 (good line) and 25% 3S= (try to stop ruffs).  Easy.
Comment: Thanks for explaining this. I saw the point of not handing out Av+/Av- without more information, but failed to convey (and properly appreciate) that more information is always available. IMO the big downside of Av+/Av- here is that we then basically ignore the bidding phase of this deal. If 3S was reached at a majority of the tables, then, fine, no biggie. Otherwise there are exactly the cases like the field playing in 4S or in 2S after better or poorer bidding judgement in comparison to this table (cannot tell which without seeing the hand, obviously).
Comment: your last comment would actually be a very good question. The answer is very long.  Short answer: you Do Not Rule - you avoid saying anything that looks like a ruling - in a judgement case until you consult.  That way lies embarrassment when your first look is wrong.  If a result has been obtained on the board (you did let the play finish, right?) it is put in as the score.  When you have determined the ruling, you present it to the players (by preference, the "losing" side first) and assign the score.
Answer: An interesting situation. I'm not a bridge lawyer, but a bit of seaching pointed me to this source.

The director should not apply the Revoke Laws. The defenders, however, may well be due an adjustment.

This is in line with my common sense. It is not a revoke, but the defenders have been damaged. Even though they, too, had a chance to count that the dummy has only 12 cards on display. I still think that the dummy and the declarer should shoulder most of the blame for the irregularity.
I would just call for the TD, and let her sort it out. Exactly what kind of an adjusted score will come depends on too many factors to handle here.
Hopefully a qualified TD shows up.


Heads up: new spam tactic

Question: Well, not necessarily brand new, but we're seeing a spate of it. Spammers are creating questions copied from Reddit, DPReview, and other sites, and then coming back a few days later to edit spam links into those questions. If you see a short question that looks... forum post-y, and comes from a new user, try a google search of the first sentence to see if it's actually plagiarized.
Comment: On [bicycles.se], we had somebody who was plagiarizing existing questions from the site, though they were posting with the spammy links already included.
Comment: I also want to note that the links don't currently resolve, so maybe the spammer's hosting provider already pulled the plug on them. This often (I hesitantly avoid using "usually") results in the spammer getting a different provider and trying again, but sometimes they get a clue and stop. https://chat.stackexchange.com/transcript/message/47144117#47144117
Comment: I just spotted this new tactic on Stack Overflow, and was not surprised to see it's spread across the SE network.
Answer: Are you (i.e. the ♦ moderators) OK with us (regular contributors, or in my case, regular passers-by) to use spam flags for such questions, even before the links are being inserted? Those spam flags will feed SpamRam, Stack Exchange's spam protection system, and if they're validated (6 flags by normal users and/or 1 by a ♦ moderator) the IP will be blocked from further posting.
Or would you prefer to be notified with a custom moderator flag? This has the benefit that you can add additional details to it, such as the source of the plagiarized content, but one could also post that as a comment.
Comment: @mattdm it's ok if it's pretty recent but then I'd flag for moderator attention only rather than spam flag.  It's always possible someone is asking in more than one place.
Comment: Hmm, the idea of posting the link as a comment isn't a bad idea either to help other users that can flag it know what is going on.
Comment: I'd say do both if you can.  As long as we have a mod flag for it we'll be able to take a look and we can always invalidate the flag (even if it has passed) after checking it out, but there is no need to wait on a mod to process.  I'd also suggest making sure it is an OLD post wherever else you find it.  It's also possible someone could legitimately post a question in more than one spot.  Please include the link to where you found it in the moderator attention flag too.
Comment: @AJ Unfortunately, it seems like sometimes it's an old post but sometimes it's pretty recent on Reddit or wherever.
Comment: @AJHenderson I just tried raising two flags for [this one](https://photo.stackexchange.com/questions/102335/what-are-some-good-resources-for-a-beginning-photographer) but it seems I can only raise one flag for a question.

Heads up: new spam tactic


Truffle: Creating a single ABI file if contracts are in separate .sol files?

Question: I am building a project which is divided into separate .sol files, one per contract or interface. The tutorial shows a single file cryptozombies_abi.js which appears to me to be something like the json of all the separate of files found in the build folder after the compile concatenated but I am not sure. My question is, is there a way to create a single ABI from multiple sol files -- I have attempted with no success the --abi option of truffle compile which does not fail but also does not produce one large ABI -- it does produce the json still (which I am guessing are in fact ABIs for each sol file).
Comment: EDIT: Not sure that the JSON created by Truffle compilation is meant to be ABI files although I think they look like ABIs.
Answer: Run solc --abi on whatever source files, and any imports will be pulled in my solc, and also compiled giving all the ABIs of every contract that was imported into that source file.
Comment: can this be done with Truffle compile? as mentioned, I tried and it does not seem to work.
Comment: I tried solcjs command line tool -- I do not see how to create a single ABI file from the ABI files produced for multiple contracts. Are they simple concatenated into a single file in a separate step?


Is there a fix for the bugged playthrough 2 in Borderlands 2?

Question: I finished playthrough 2 quests with my friends all out of order and it seems that my playthrough somehow got forever stuck on playthrough 2. I have no story missions left and if I accept new side quests they are not scaled to level 50, like they would be in playthrough 2.5. The last story mission I had to do was "Data Mining", has anyone else encountered the problem and do they know a way to fix it?
Answer: when you are at the main menu hit Y if you are on the xbox and re click to load the character you have already loaded. When it reloads it will ask you if you want to play true vault hero mode or normal mode. Click normal mode and you will be back to play through one and have your situation fixed.


Since slow hard drive is the item that makes a notebook slow, will SSD completely turn the table on speed?

Question: By using a top-notched SSD (solid state drive), can a notebook feel faster than a desktop computer?
Comment: I don't know where you're getting this idea that notebooks are slower than desktops. My laptop *smokes* my desktop.
Comment: This is very subjective... perhaps you should be more specific about what you're comparing.
Answer: You would notice a performance difference in the laptop.
However other factors such as processor speed, amount of memory, motherboard will determine how much a difference it will make.
A slow processor, low memory and low-end motherboard etc the difference will be less obvious.
My laptop is far faster than my desktop even though it has a slower hard drive (5,400 RPM compared to the desktops 7,200 RPM).
It depends on what the spec is but having a SSD will improve the laptop speed and reliability if it's being bashed about a bit.
Answer: If you are using Windows 7 ensure the hard drive is the slowest component on your system by comparing the 5 results from the Windows Experience Index.
If your hard drive is the slowest component then it might be worth upgrading the hard drive.
I upgraded from a 5400 rpm to a 7200 rpm drive on my laptop and it only increased the score by 0.3


Potty now means playtime for my 3 year old son

Question: My wife and I have been trying to potty train my son for a few months now to no avail. He did a lot better when we first started training him, and now it seems his progress has gone backwards.  Let me explain...he has had a plastic training potty since he was two, and around that time he pretended to go while wearing his normal attire - just for play.  We thought he was too young for us to seriously try to train him, but nonetheless, he had the concept.  Fast forward to when he turned 3.  We bought an adapter seat to use in our bathroom.  We explained what it was for and he seemed to understand.  Whether it was pure chance, or by habit of having to go when he wakes up in the morning, he was able to pee using the adapter seat and also the plastic potty a half dozen times.  Then, my wife was able to get him to poo.  This was within a few weeks after he turned 3.  We decided to get serious and try underwear.  That did not work so well.  He was not able to tell us before he had to pee or poo, just immediately after when it was too late.  He does not seem to know how to tell us before he has to go.  Now were trying to predict when he has to go and taking him to the potty.  This hasn't worked that well because he doesn't seem to have to go and ends up playing with the water in the sink or unraveling the toilet paper.  Every-time we take him (upon suspicion of having to go), it ends up being playtime.  How can we get our son to tell us before he has to go?
Comment: Kids are awesome.  Everyone should experience raising them!
Answer: TL;DR: There are several signs of toilet readiness, and multiple methods of toilet training, supported by research, that may be useful for your child. See the book and the links below on Azrin and Foxx's method.
In my experience, if the child can recognize full bladder and can follow simple directions, then the child is ready for potty training. From your description it sounds like your child should be ready. I recommend starting from scratch using the method described in the book below.
This book describes how to quickly potty train kids, by the original researchers who developed the technique. The technique, with minor variations, is still used today. We used another approach with our older child, and it took a while. Then we used this method with our younger child, and it worked well.
Toilet Training in Less Than a Day, by Nathan Azrin, Richard M. Foxx:
https://www.amazon.com/Toilet-Training-Less-Than-Day/dp/0671217011/
SEE ALSO:
Parenting Science blog ( https://www.parentingscience.com/ ) has useful discussion of many parenting related topics, including different techniques of toilet training. For example, see the quote below from this post: https://www.parentingscience.com/toilet-training-techniques.html

[Azrin and Foxx's] toilet training techniques [...] include:

teaching through pretend play
positive reinforcement (food rewards)
practice drills, and
overcorrecting for accidents.

Prerequisites
Azrin and Foxx also emphasize the importance of timing. Not all kids
  are ready for their approach. In their book, Azrin and Foxx specify
  that kids should be 20 months or older, and they should meet several
  developmental criteria. In particular, kids should be able to

sit up by themselves
walk
stay dry for a couple of hours at a time
imitate
recognize a full bladder
point to body parts that you name
retrieve objects for you, and
follow simple instructions like "put the doll on the potty."

Kids should also be able to pull a pair of loose-fitting underpants up
  and down by themselves. (For tips on how to help your child learn
  these skills, see my article on potty training preparation.)
There are medical and emotional criteria, too. Parents should also
  avoid these toilet training techniques if children are ill,
  constipated, or uncooperative.
Last but not least, Azrin and Foxx warn that their toilet training
  techniques require a lot of preparation. The title of their book
  ("Toilet training in less than a day") is a bit misleading. To be
  successful, a parent must do his homework.
So—as you read my brief summary below—-keep in mind that this is not a
  substitute for reading their book. If you want to try fast-track
  toilet training techniques, the Devil is in the details. Without
  adequate preparation, you risk failure. And even worse—you risk making
  your child resistant to other attempts at potty training.
Bottom line? No parent should attempt this method without first studying Azrin and Foxx's book.


How to validate that an object (whose locator we don't know since it is not present) is not present in a page

Question: Let's say I want to verify that an upload button is not present in a page. I cannot use any locator here since I don't know the object locator value. So how do I assert in my test that it is never present?
Comment: Possible duplicate of [How to assert that particular element is not displayed?](https://sqa.stackexchange.com/questions/39018/how-to-assert-that-particular-element-is-not-displayed)
Comment: Saurav, do you mean the button is **never** present? If not, you can either use the locator is should have if it was there and check for the not displaying. If that's the case, I can make it an answer, placing the code.
Comment: Is there a *specific button* you want to check the absence of? If so, why don't you know how you'd locate it if it was present? If not, why are you testing that an unknown button isn't there; why *might* it be?
Comment: I think this question is more general and better left open than the downvoted code and error dump that the linked question basically is. I'm voting to leave this one open and close the other as a duplicate of this one.
Answer: Normally "upload button" is a HTML input of type file which looks like:
<input type="file" ...... >

So you need to verify whether at least 1 input of type file is present at the page. It can be done using the following XPath selector:
//input[@type='file']

Example code (Python)
file_upload_elements = driver.find_elements_by_xpath("//input[@type='file']")

if (len(file_upload_elements) > 0):
    print('File upload input is present')
else:
    print('File upload input is absent')

Answer: In my opinion, there is no such thing as I can not use any locator here. An (assumed) upload button is part of the DOM and can be located in some way.
Maybe the button is always in the same place, so you can check if By.css(".container button") is present. Maybe you can ask the devs to provide a better locator. Or you could count the visible buttons on the page, maybe these are pretty constant so a +1 change would mean the button is present.
If maybe the button text is always the same you could use something like driver.findAll(By.css("button")).stream().filter(e -> e.getText().equals("buttontext")).count() == 0
There are definitely more ways, but I hope these ideas give you a direction.
Answer: Using Java
 boolean textPresent = false;
 try {
 if(driver.findElement(By.xpath("//*[contains(text(),'Update')]"))){
   textPresent = true;
 } catch (Exception e) {
   textPresent = false;
 }

Using Ruby with capybara
expect(Capybara.current_session).to have_content('Update')


Is GPG suitable as part of a password manager and generator?

Question: I assume that GPG is very strong to crack, guess, etc. Since I have confidence in GPG, would it be appropriate to use my GPG key as the master key for a password manager or generator?
Comment: Well, it makes some sense. GPG is a trusted, vetted product that you have a reliance on. That's one of the greater tenets in choosing a security product. This is why we seek experts to answer these questions, because unless you've spent a lot of time and are well-versed, that's all you have to rely on. So, after some thought, +1 from me.
Comment: why vote down? noobish question?
Comment: There is no practical usage for using your private key to decrypt a password manager with GPG. Plus it sounds like a product recommendation.
Comment: It sounds clever and secure to me. What's wrong with product recommendation? I've seen other questions about password managers etc.
Comment: @ttouch Ah see, that *to me* part is the key point.
Comment: How do you find a password manager with GPG easy? Basically you would have to keep your private key stored on your phone, linux machine. That doesn't sound really safe.
Comment: but if my GPG key is my digital signature, I _have_ to carry the key with me EVERYWHERE.
Comment: Sure but you need to secure your key too right?
Comment: ... which you would protect using a password, which would be symmetric encryption, which you should use directly to encrypt your password manager database, yes? Longer answer below.
Comment: thank you Jeff. my question seems pretty dumb. Didn't thought of it that way :P
Comment: as you said we could use the symmetric part of GPG as-is (and not a variant)
Comment: I think you could effectively make use of GPG and git (for sync), and really it **would** make sense if you had an external smartcard that held your key. It'd even work with Android if said card were NFC.
Comment: If I had an NFC I would do it. thought of it SO many times. not as pass manager, but as pam module for system authentication. but is NFC safe?
Answer: GPG encrypts your data with a symmetric key, then encrypts  that symmetric key with / for the public / private keypair. That keypair is usually kept safe by symmetrically encrypting it.
What you're asking for is a program that would diagram as such:
Symmetric -> Asymmetric -> Symmetric

What you should use is a password manager that does the following step:
Symmetric

The job of a password manager is as much one of not placing your data in cleartext as it is simplicity. GPG's job is to allow communication of a key exchange across a clear channel. Since you'll be the only one encrypting / decrypting your passwords, symmetric encryption is just fine. Cryptographically speaking. GPG uses OpenSSL for the backend anyway as a great number of freely available password managers most likely do.
Now, with all that said, it makes good sense to do this on your computer if your GnuPG key is held on an external smartcard, and it'd work with a phone if there were an NFC version of the card. You could use git for synching various password files.
Comment: So, lets say I have a simple setup (bash script) that just encrypts my passwords in files and decrypts them. Should I use AES (maybe with many iterations) or GPG? Which is more secure?
Answer: I'll start with the quick answer to your question (which has two parts). First off, yes, GPG is suitable as a password manager in terms of having strong encryption. It is very unlikely (most would say impossible) that the password would get cracked using asymmetric encryption.
The second part of the answer is that, no, it's probably not suitable as a password manager. Having to manage keys can be irritating if you're using several machines, and if you lose your private key, you're liable to have to reset many, many passwords--a real pain.
The quick solution to the key management problem is to use gpg -c, which allows you to use symmetric encryption with gpg using a passphrase. This is great, but now we're getting into the territory of what I'd actually recommend for an alternate solution since you're not actually using the primary benefit of GPG anymore (public/private keys).
I'm not going to go into the full details of my current setup, but I can outline it quickly: rather than using gpg to manage a text file of credentials, I use openssl. The reasoning behind this is simple: almost every Linux (and, I believe, OS X) system comes pre-installed with openssl. It's universal, which makes portability very easy if I'm carrying my encrypted file around with me on a flash drive (a copy of it, of course). There are no keys to manage, and I can easily choose which encryption method to use.
I tend to prefer something like this: openssl aes-256-cbc -salt -in passwords.txt -out passwords.aes to encrypt my password database. Don't forget to rm the plaintext! From there, I can easily just run openssl aes-256-cbc -d -in passwords.aes and grep for the creds I'm using. Adding things can get a little bit trickier--I generally have to print out to stdout, or append a temp file then re-encrypt--but it's worth it to me for the portability that openssl provides.
Comment: very smart! is the aes strong enough?
Comment: AES-256-CBC should be strong enough for any feasible purpose. The real risk would lie in brute-forcing the password, rather than breaking the crypto itself. Using a long, complicated passphrase is the way to go on this one.
Comment: Is it stronger than GPG?
Also, a note about portability: Do not EVER decrypt your passwords on PCs that are not entirely yours. Reading the memory/keyboard/usb drive is very easy and one could steal your encrypted keys AND your key.
Comment: One advantage of using gpg in this setting is that it authenticates the encrypted files and can detect if the encrypted file gets corrupted or tampered with. Openssl, on the other hand, only encrypts the file.
Answer: Yes, and in fact there is such a password manager, that uses gpg for the encryption.  It's called pass, and it's available at http://www.passwordstore.org/ for linux/Unix.

With pass, each password lives inside of a gpg encrypted file whose
  filename is the title of the website or resource that requires the
  password. These encrypted files may be organized into meaningful
  folder hierarchies, copied from computer to computer, and, in general,
  manipulated using standard command line file management utilities.
pass makes managing these individual password files extremely easy.
  All passwords live in ~/.password-store, and pass provides some nice
  commands for adding, editing, generating, and retrieving passwords. It
  is a very short and simple shell script. It's capable of temporarily
  putting passwords on your clipboard and tracking password changes
  using git.
You can edit the password store using ordinary unix shell commands
  alongside the pass command. There are no funky file formats or new
  paradigms to learn. There is bash completion so that you can simply
  hit tab to fill in names and commands, as well as completion for zsh
  and fish available in the completion folder. The community has even
  produced a GUI client, an Android app, an iOS app, a Firefox plugin, a
  dmenu script, and even an emacs package.
Comment: Yea, I'm currently testing it, but I'm not sure if GPG encryption is more suitable than AES or Serpent...
Comment: Under the hood, GPG is using AES or a similar symmetric cipher for the bulk of the encryption.  A random session key is generated for the symmetric algorithm, and that key is encrypted using RSA or other asymmetric encryption.
Answer: To read my passwords I use an encrypted file in my home directory. To decrypt it, I simply use the decrypt command of GnuPG, covered in a nice shell script rpw (for read passwords) - it then asks me for a pass-phrase and displays all my passwords in the terminal. Optional, I can give a search term like e.g. rpw ebay. Then only the line, where 'ebay' appears, when I give out the passwords. Please find my script from /usr/local/bin/rpw here:
gpg -d -o - /home/USER/pw.gpg | grep "$1"

To write/ edit the password file, I decrypt it, edit it, and then encrypt it again, while wiping the decrypted file. Here is this script, which is called wpw (for write passwords). /usr/local/bin/wpw:
gpg -d -o /home/USER/pw_unenc /home/USER/pw.gpg
vi /home/USER/pw_unenc
gpg -o /home/USER/pw.gpg -e /home/USER/pw_unenc
wipe -f -s /home/USER/pw_unenc

This is all very easy and relies on GnuPG's security.
Comment: There be a [Vim plug](https://github.com/jamessan/vim-gnupg-in) for editing encrypted files. It may also be possible to have Vim read from standard-in with `gpg -d -o - /home/USER/pw.gpg | vim -` and when done editing, run the encryption command during Vim's write process with `:w !gpg --encrypt > /home/USER/pw.gpg` then quit without re-saving Vim's buffer with `:q!` ... though the aforementioned plug-in is likely a more robust solution, sometimes modifying the host isn't an option.


Is there a frosting similar to whipped cream but without cream?

Question: Can I use butter or margarine for frosting instead of whipping cream in cakes?
I tried frosting cake with butter and icing sugar but I did not like the outcome.
Is there something else that'd come out similar to whipped cream without using cream?
Comment: What did you do with the butter to turn it into a frostig?
Comment: Important to note, also, that butter and margarine are different.
Comment: What kind of frosting texture are you looking for? Something like whipped cream, but without cream? Or do you just not like whipped cream as frosting so you want something different? There are a lot of frosting recipes out there, not much point trying to fix a failed buttercream frosting if that's not what you want anyway.
Comment: I added icing sugar to  margarine and then beat for some time @stephie
Comment: Can you tell us what you didn't like about the outcome?  And perhaps some specifics about the amounts you used?  It would help to know what didn't work (and why) before trying to figure out what will work.  Frosting from butter and sugar is going to be different from whipped cream - that difference might be the problem, or it might be that you need to improve your frosting recipe.
Comment: Yes, something like whipped cream but without  cream. That kind of texture.
Answer: There are dozens of different types of frosting.
Whipped cream frosting is one of them. It's made very simply by whipping heavy whipping cream until it reaches stiff peaks and then adding a tablespoon or two of sugar to help stabilize it. It is light, airy, and not particularly stable for long periods of time unless it is kept in the refrigerator.
Another very common type of icing is "buttercream" frosting. There are several different kinds of buttercream but the most simple kind is made out of butter whipped together with lots of powdered sugar and a small amount (a tablespoon or two) of liquid - either milk or even various types of alcohol if you want your icing to be boozy. It can be made with most solid fats including margarine or shortening.
Buttercream is pretty stable without being refrigerated but it will not have the same texture (it's more dense and "fatty"). It sounds like you're used to the former but you tried out the latter and you weren't happy with the results - which I understand - it is generally significantly sweeter because you're using cups of sugar instead of a few tablespoons as with whipped cream icing.
If you want to try something that's a bit in between these two products - that has the light, airy texture of whipped cream but is sweeter and doesn't use cream, you might consider trying a "seven-minute icing". It's a cooked, egg-white based icing that is similar to meringue. It's made with egg whites, sugar and cream of tartar (as a stabilizer). Done correctly, it makes lovely fluffy peaks with a shiny gloss.
Answer: If what you're looking for is a close substitute for whipped cream frosting, that narrows the possibilities down.
Boiled frosting is made with a sugar syrup (with cream of tartar and other flavorings) which is boiled and added to whipped egg whites which set with the residual heat.  It is a light and fluffy frosting which contains no fats.
Meringue style frosting is made with whipped egg whites and sugar (and other flavorings) which is then heated over a double boiler to set the egg whites.  This frosting is thick and fluffy, though it will deflate over time unless baked.  French style meringue frosting is supposedly left uncooked, which may change the flavors.
You might also want to look at Royal icing, made with meringue powder or egg white and powdered sugar, which does not require cooking, and will have a similar flavor profile to boiled or meringue style frosting.  However, the texture is not fluffy but smooth, and it tends to be dried hard, and used for structure or decoration.
For textural purposes, you won't find a better match for whipped cream style frosting than whipped egg white based frosting.
If you're looking for flavor profile rather than texture, you might try a simple powdered sugar icing that's thinned with milk instead of water (possibly with a small amount of butter for flavor).  Something like this might work well, with both butter and milk in the mix, though you can certainly tweak your proportions to your taste.  Or something like this recipe which includes flour and egg white along with butter, milk and sugar for a complex frosting recipe that might be less sweet.
And, finally, you might look at marshmallow creme frosting, which includes butter, marshmallow fluff, sugar and milk, and which should be light, fluffy, and sweet.  There are also variations which include actual marshmallows instead of fluff, melting them into something like a boiled icing recipe, or into a cream and sugar mix.
Other frosting recipes might not be a good match for your preferences - the recipe you didn't like, of margarine and powdered sugar, seems very similar to a buttercream frosting recipe, which is thicker, sweeter and richer than whipped cream frosting.  Likewise, cream cheese frosting (similar to buttercream with butter, sugar and milk in addition to the actual cream cheese) is less sweet, but tends towards creamy, dense and smooth rather than light and fluffy.  And ganache frosting, made with chocolate and cream, is flavored, denser, and requires the missing ingredient (cream) itself.
You might check out the European style buttercream frostings, though, as they are lighter, fluffier, and less sweet than the American version - both the swiss and italian are close to a mix of meringue and boiled style frosting (respectively) and buttercream.  The french version, on the other hand, uses egg yolks with the sugar syrup and butter for a richer flavor.
Answer: There are products specifically created to imitate whipped cream. They consist of modified starch with added sugar and flavoring, sometimes also color. You mix them with cold milk and whip. The texture is the same as whipped cream, the taste is rather close.
Anything else that you try is simply another frosting - it can be tasty, but nobody would mistake it for whipped cream. It would be up to you to decide if a frosting is sufficiently "like" whipped cream or not.
Comment: Do  you mind giving a list of these products that imitate whipped cream?@rumtscho
Comment: I don't have such a list.
Answer: Chilled, full fat coconut milk can sometimes be whipped (with sugar and the kind of stabilizers that are also used with cream); how well it works will be very dependent on the brand used and your exact method, so experimentation will be required.


Formally smooth maps between adic rings and regular immersions

Question: Suppose $(A,\mathfrak{a})$ and $(B,\mathfrak{b})$ are two adically complete (commutative) noetherian rings. Let $f:A \to B$ be a continuous formally smooth formally of finite type map (that is, $B/\mathfrak{b}$ is a finitely generated $A$-algebra). In this case it is proved in EGA IV that $\Lambda_{\mathfrak{b}} \Omega^1_{B/A}$ is a projective module of finite rank, where $\Lambda_{\mathfrak{b}}$ denotes the $\mathfrak{b}$-adic completion functor.
In a (not nessecerily) adic case, if $f:A \to B$ is formally smooth and of finite type, it is proved that there that $f$ is actually smooth, so that letting $I = \ker (B\otimes_A B \to B)$, we have that $I$ is locally generated by a regular sequence (from which it follows that $\Omega^1_{B/A} \cong I/I^2$ is locally free).
Now, to my question: Again, assume we are in the adic case as above. As seen above, the module of Kähler differentials, $\Omega^1_{B/A}$ is no longer the "correct" object, but its completion is.
Set $\mathfrak{b}^e = \mathfrak{b} \otimes_A B + B \otimes_A \mathfrak{b} \subseteq B\otimes_A B$, and let $J = \ker( \Lambda_{\mathfrak{b}^e} B\otimes_A B \to B)$. Then we have that $J/J^2 \cong \Lambda_{\mathfrak{b}} \Omega^1_{B/A}$. Is it true that $J$ is locally generated by a regular sequence? that is, is the map $\Lambda_{\mathfrak{b}^e} B\otimes_A B \to B$ a regular immersion?
Thanks!
Comment: Have you checked http://arxiv.org/abs/math/0604241v1? (It is published in Comm. Alg.)
Comment: Thank you for your comment. Unfortunately, I could not locate this result in this reference.
Answer: See Commun. Algebra, 22(1994), 4801-4805.


Slow motion of a spherical object on an blunt slant obstacle

Question: In cocos2d environment and box2D when an spherical object falls on a blunt slant obstacle, it moves really slowly, that's nauseating, if you have coded to not to have any interaction with world while object is in motion. Is there any way to get rid of this slow motion of object?
Comment: Can you describe in more detail what is happening, and what your desired result is? A quick picture or sketch would be helpful as well.
Answer: It's possible that your slant really is not steep enough as Aku says, but it's more likely you flagged the object for fixed rotation, meaning it's not rolling down the slope, but rather sliding against friction. This makes it much slower, and if the slope is not steep enough, can halt it entirely.
Answer: Physics dictates that when you put a ball on a slant, it tends to roll. If it's a small slant, it rolls slowly. It's a matter of certain physics applied to certain conditions.
To get the effect you want, you have to either change the conditions...

for example, increase the slope to get it to roll off quicker

... or change the physics...

for example, add more friction (this could be conditional; only added if the slope is very small).


Who introduced the "dagger"symbol as conjugate transpose in quantum mechanics?

Question: The $\dagger$ symbol is often used in quantum mechanics,and also often in general mathematics to represent the conjugate transpose operation.For Hermitian matrices we can write $$A^\dagger=A$$Who introduced this notation?
Comment: Someone who shouldn't have (editorializing here) since it's difficult to tell from a plain old "t" to those of us with aging eyesight.
Comment: Who introduced this in QM literature, or generally in the mathematical literature?
Comment: Actually interested to know about both!
Comment: I would have thought that Dirac's 1939 paper "A new notation for quantum mechanics" was the answer, but I was wrong.  In fact, a cursory search of my library's bookshelves shows no QM books by big-name authors using this notation (Pauli, Dirac, v Neumann, Landau and Lifshitz).  I'm sure there's examples, but it would be nice to have a particular instance.
Comment: @ConsigliereZARF Very good!
Answer: In a now-deleted comment,  Consigliere ZARF listed a number of papers published in Zeitschrift für Physik in the late 1920's that used this notation.  The earliest was Pascual Jordan's 1927 "Über eine neue Begründung der Quantenmechanik", using the notation on pp.816-817; with about 10 other papers published in the following few years, all in the ZfP, all behind a paywall.
According to Duncan and Janssen "(Never) Mind your p's and q's:
Von Neumann versus Jordan on the
Foundations of Quantum Theory", p.57, the Jordan paper was where the notation was introduced.  The paper "Über die Grundlagen der Quantenmechanik" by
D. Hilbert, J. von Neumann, and L. Nordheim, Mathematische Annalen (1928) uses (on page 19) $A^+$ for the adjoint of $A$.
Up to the point reading Consigliere ZARF's comment I had focused on English-language literature, which seemed to lag about a decade behind the German.  The rest of this post describes what I found there.
An approximate answer: Google books search for "dagger+Hermitian"  led to these early uses of the notation.
Page 59 of W. H. Furry's 1938 "Note on the Theory of the Neutral Particle",
Phys. Rev. vol 54, p.56  has this:

In dealing with such matrices we shall use
  an asterisk (*) to indicate the complex conjugate
  matrix, a prime (') to indicate the transposed
  matrix, and a dagger ($\dagger$) to indicate the Hermitian adjoint matrix.

which seems to me to be an indication that this notation needed explaining.  A few years later, Booth and Wilson, in "Radiative processes involving fast mesons" (Proc. Roy Soc A, v175, July 1940) wrote this in a footnote on p.487:

Note that in order to
  conform to the usual custom we modify Kemmer's notation and use a dagger to denote
  the Hermitian conjugate.

indicating that the notation had by then become standard (although not universal, or else Kemmer's notation from the year before would not have needed adjusting).
For all I know, it is possible that Furry was the true original introducer of the dagger notation.  It is certain that the notation was in use in the late 1930's.
Added: Furry cites an earlier paper of his (Phys Rev v51, p.125 (1937) and another by Pauli ("Contributions mathématiques à la théorie des matrices de Dirac", Annales de l'institut Henri Poincaré, Volume 6 (1936) no. 2, p. 109-136) , that use a superscript plus sign $A^+$ for the same thing.  Page 119 of Pauli's paper has

En général, nous désignerons par $\gamma^{+\mu}$ les matrices conjuguées hermitiques (transposées et conjuguées) des $\gamma^\mu$

and so on, with what I think is a typo in the next bit: "(c'est-à-dire telles que $\gamma^{+\mu}_{\rho\sigma}=\gamma^{*\mu}_{\rho\sigma}$)".
The leap from superscript $+$ to superscript $\dagger$ is understandable. It was taken, for instance,  by Pauli in his 1943 paper, "On Dirac's New Method of Field Quantization", if not earlier. (See equation (4) on p.176.)  But not, evidently, by Schwinger in his 1948 paper "Quantum Electrodynamics. I. A Covariant Formulation", who uses $C^+$ for the Hermitian conjugate of $C$, on p.1441.
Comment: This paper https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.1938.0058 (written in 1937) uses the notation on p.261.  So probably Furry did not introduce it in his 1938 paper.


Significance of modular arithmetic in DFT?

Question: In what ways does modular arithmetic plays a part in DFT?
Why is it a so integral part of DFT?
Answer: This answer to a differently worded question answers your question also.
And this answer is relevant.
And this answer and this answer.
I confess that I take great exception to anyone who denies that the Discrete Fourier Transform (and inverse DFT) fundamentally periodically extend the finite set of data presented to it.  I'm a nazi about it.  The DFT assumes that the $N$ samples of $x[n]$ passed to it are one period of a periodic sequence where $x[n+N]=x[n]$ for all integer $n$. And the inverse DFT does the same in that the $N$ samples of $X[k]$ passed to it are one period of a periodic sequence where $X[k+N]=X[k]$ for all integer $k$.
The modulo arithmetic done to the indices of $x[n]$ and $X[k]$ simply guarantee this periodicity while also guaranteeing that neither index, $n$ or $k$, go outside of the bounds of the finite sized arrays in memory representing $x[n]$ and $X[k]$.  That is
$$ 0 \le n = \operatorname{mod}_N(n+mN) < N $$
and
$$ 0 \le k = \operatorname{mod}_N(k+mN) < N $$
for any integer $m$.
Answer: You might find the answers to this related question pertinent as well:  In case of Complex DFT spectrum, why the x axis range from N/2 to N point mean a negative frequency?  (Check out my answer in particular.)
If you really want a different conceptual understanding of the DFT and its modular nature, read my blog article:

DFT Graphical Interpretation: Centroids of Weighted Roots of Unity

I think r b-j's answers to this are correct, but not as helpful to someone trying to learn it for the first time.  He puts "outside the box" and "inside the box" all in one compact definition.
The key is understanding that the forward and reverse DFTs are essentially the same mathematically, and they operate on a finite domain with a finite range.  In each case, if you extend the range of the operator "outside the box", by extending the underlying trigonometric functions, you get a repeat pattern.  Thus, if I choose a segment of a signal, called a frame, and apply the DFT to it, I will get a set of complex values which Macleod calls the DFS (Discrete Fourier Spectrum).  The repeat pattern in the frequency domain is associated with what are known as "Aliases" and is associated with (and proven to be a good description) by the sampling theorem.
Going in the other direction.  If you take a DFS, and apply the inverse DFT, you will get your original signal frame back.  If you extend the trigonometric functions in this case, the signal produced with be a repeat pattern of your sample frame.  The only signals for which the repeat pattern matches the actual signal is for periodic signals where the frame size is a whole number of periods.
The repeat patterns are why modularity is inherent.

This blog article by Neil Robertson is specifically on this topic:

Demonstrating the Periodic Spectrum of a Sampled Signal Using the DFT


What mistakes have you made while restringing and setting up a Floyd Rose guitar?

Question: I have a Schecter Demon 6 with a floating Floyd Rose and this is my first time restringing it. I want to ask you guys for any headups, recommendations, mistakes you did while doing this?
Comment: Like with any guitar, re-string only one string at a time.
Comment: This may get closed for being off topic but... It's funny you should ask.  I turned it face down and some metal cubes fell on the floor.  The best thing I did, take in to a tech to restring it for me.
Answer:
What mistakes have you made while restringing and setting up a Floyd Rose guitar?

In 1990, I left some oil heating up in a frying pan in the kitchen, while doing up a Floyd Rose bridge in another room: not just re-stringing, but intonation.
Luckily, I had the ensuing fire put out before the firemen showed up.
Minor damage to a few cabinets, and a ceiling repaint. The intonation, as such, as fantastic though.
In terms of mistakes in the actual restringing and setup, I have one main regret: in younger years I used crappy strings with poor tuning stability. That not only wastes your time due to all the adjustment needed after the restringing and setup, but is bad for your hardware, because it requires too much fiddling with the tuners, as well as unlocking and re-locking of the locking nut, which wears down the parts.
Answer: If you want an easy time, go one string at a time, and put the same type/gauge of string on it that you had before. Changes in string gauge/tension will require a bit of care to fix, like I recently answered here: Floyd Rose in Standard Tuning with .011 gauge strings
Aside from that, most Floyd Rose style bridges are not set up for ball end strings. That means you have to cut the ball end off to lock the string into the saddle's locking mechanism, and then cut the string to length on the headstock end. Take care with that step: measure twice, cut once! Don't leave yourself with a string that's too short to tune.
Also, I find it helps to reset all the fine tuning screws (they usually sit behind the saddles) to their midway point, before I get the tuning finalized and the nut locks back in place. It sucks to be "done", then realize you can't quite tune a string properly, and you don't have enough travel left on the fine screw to fix it. Allen wrenches back out, undo the nut locks, re-tune, etc.
There's a lot of moving parts in those Floyd Rose bridges. Try to think things through first before doing stuff: work smart, not hard.


Can I use this spray gun with my air compressor?

Question: I have a spray gun that needs 4.4 cfm and 60 psi to work. My compressor is only 2.6 cfm but 135psi with a 6 gallon tank and a 2hp engine. Will this setup work to spray paint?
Answer: Sounds like you're using an automotive sprayer. You need to set your compressor's regulator to 60 PSI max or the can may explode. If the compressor doesn't have an adjustable regulator, you'll need to install one.
Answer: It should work fine until the tank runs low. Then you go and refill your coffee until the compressor catches up.


Did LEGO ever make bricks without the LEGO logo?

Question: While sorting my LEGO collection I found bricks with two different fonts and many without a font at all. I also found Tyco and Mega Bloks bricks. So did LEGO ever make blank bricks?
Answer: Yes and no. If you found normal basic bricks without the LEGO logo, then they are definitely not Lego.
However, some parts are too small to have the logo. Things like utensils from the Friends theme, balls, technic pins, etc. don't have room for the logo, but this doesn't mean they aren't made by Lego.
The very first Lego bricks (2x2 and 2x4 bricks in 1949) also didn't include any logo or markings on the bricks. They also had completely hollow undersides, and slots in the side walls. But I suspect this is not what you have.
As for the bricks with two different fonts of LEGO, these may be made by Samsonite (under contract with Lego) in the 60s–80s. They were notoriously careless with keeping the logo straight on the stud, or even having the same type of logo on multiple studs on the same brick :)
Comment: On closer examination the blank bricks seem to be Tyco.  They both have a number stamped in the underside button.  I've separated them to our kiddie toy box.  I don't plan selling bricks but do the older bricks have any value?  Thank you Ryan for your prompt answer.
Comment: As time marches on, Lego has (usually) become more aggressive with putting their name on pieces. Technic pins definitely have it now. Soccer balls do too. Even 1x1 round bricks finally do. Just today I found the Lego logo on the clip of a tiny Friends pen.


Why do the opposing sides of a D20 generally add up to 21

Question: Most D20s I own (with the exception of poorly made foam ones or MTG spin-down dice) seem to have all opposing sides add up to 21 (20 + 1, 15 + 6, etc).  Why is this?  Who started this?
Comment: You'll notice this on most other dice, too: a d6, a d8 and many others follow the practice of putting the highest number opposite the lowest, the second highest opposite the second lowest, and so on, so that any given side added to its opposite adds up to the same number as any other choice.
Comment: D6 always add up to 7 too. You have to arrange the face some way, and having opposite faces add up to N+1 seems to be the traditional way.
Comment: [D20 sides](http://dicecollector.com/images/D20.PNG)
Answer: Opposite sides add up to 21 on a d20 for the same reason that opposite sides add up to 7 on a d6: if there's a manufacturing or design defect, and the die ends up slightly flatter than intended, then the average result of the die will not change.
Consider a d6 that ends up a bit flat: two sides opposite each other will both have an increased chance of being landed on. But since these two sides' numbers are "opposite" to each other, they will not affect the average of the die. For example, a d6 might have a 1/3 chance of landing on a 1, a 1/3 chance of landing on a 6, and, and a 1/12 chance of landing on each of the other faces. The average of this seriously-deformed die is: 1 * 1/3 + 2 * 1/12 + 3 * 1/12 + 4 * 1/12 + 5 * 1/12 + 6 * 1/3 = 3.5, the same as a normal die.
Of course, various other deformities (malformed corner, air bubble in the plastic, some enterprising fellow put a little lead in the die, etc.) will still play merry hob with the probabilities in an unfair way, but a flattened die will be somewhat fair in that its biases favor both high and low numbers equally. The layout for d8, d10, d12, and d20 dice were probably created from this same idea to make the dice somewhat fair if they're flattened.
Answer: I may be misinformed, however my understanding of the situation is that this is a result of trying to normalize the value of each region on the d20.
The best comparison is between an MTG spindown (where the numbers count down from 20-1 in sequence spiraling around the d20) and a regular d20. A spindown has all the high values clustered at one end, and the low values clustered at the other. with practice, you could easily learn to roll a spindown to get 10 or more the vast majority of the time, for a regular d20 this is impossible as the numbers are spread evenly, so high numbers are surrounded by lower numbers.
It is very hard (if not impossible) to roll a d20 for an exact individual side, so spacing them out in this way is the best way to "balance" the values, such that a practiced roll aiming for 20 has a high chance to land on much lower numbers that are adjacent, where a spindown would have other high numbers adjacent.
by laying out the numbers such that all sides add up to 21, you give a memorable way for users to navigate a d20, whilst also giving a reasonable (if not optimal) proportionality in value accross the areas of the d20.
as for who started it, I couldnt answer that, d20 themselves have been around since the Romans (http://www.wired.com/geekdad/2008/06/what-version-of/), but I can find no information on who decided the numbering scheme.
Comment: This explains the scattershot distribution, but it's orthogonal to the specific 'opposites add up to N+1' question; you could easily put 11-20 on one hemisphere and 1-10 on the other and still satisfy the opposites adding constraint (in fact, a lot of older spindowns do this).
Comment: I see what you are saying, Paul Marshall's answer seems to cover that aspect quite well, so I wont try and repeat it.
Answer: The tradition of numbering a d6 with 1 opposite 6, etc. goes back to the Ancient Greeks, if not before. As far as I know, the original reasoning behind that numbering isn't really known. It is, however, a way to improve fairness for a slightly flattened die, as noted above.
Other defects such as voids could cause a particular region of a die to preferentially land facing up. In order to minimize the effect of such defects on fairness, dice would ideally have the faces surrounding a vertex (a point where three or more faces come together) summing to the same number. Bob Bosch, Henry Segerman and I have just produced such a numerically-balanced d20 for the first time. For more details, please visit http://thedicelab.com/BalancedStdPoly.html.
Answer: Another reason might be that originally 6-sided dice used little holes to mark the numbers. The material removed to create a 6 is more than that to create a 1. As such, the different sides of a die had different weights. To balance the weight across all three directions of the die, opposing numbers were chosen to balance out the different directions. The material taken out of 6 and 1 would be the same weight as the material taken out of 5 and 2, and 4 and 3. All three directions would lose material equal to 7 holes. This, combined with distributing the numbers as far as possible from one another would lead to the current distribution of the numbers on a 6-sided die. However, on dice with more than 6 sides, the sum rule would not be enough to guarantee that all numbers are as far as possible from each other. Also, on 20-sided dice, numbers are not usually created by holes but using digits. As such, the material argument doesn't hold anymore.
Comment: Is the total amount of material removed on each axis really the relevant quantity? Wouldn't removing some material move the center of gravity towards the opposite end, meaning that it's really the _difference_ between the amount of material removed from the opposing sides that matters for balance? Hence, putting 1 opposite to 6 would _maximize_ the offset on that axis as far as the COG is concerned. And the closer the COG is to the side opposite 6, the more the die is weighted towards the 6...


Scrum of Scrum of Scrums

Question: What's the exact definition of this concept? Is it about a forum where multiple scrum masters working on a large product sync up their status or is it a brainstorming like session where multiple scrum masters working on multiple projects / products gather and share their process improvements, etc... ?
Comment: What has your knowledge gathering via your favorite search engine brought to light? What about that prior research is unclear to you?
Comment: What scaling framework are you using? Scrum of Scrums is seen in Large Scale Scrum (but, per their guide. is not a part of LeSS and isn't recommended) and Scrum@Scale. SAFe also includes an event called Scrum of Scrums, but it's defined differently than the one in LeSS. Depending on what scaling framework you're using, what the Scrum of Scrums is supposed to be may vary, and your organization may even have a different definition than these two scaling frameworks.
Comment: @ThomasOwens Thank you for clearing out that concern. I wasn't aware that different scaling frameworks define this concept differently.
Answer: I'm not aware of any authoritative answer to this question. In fact, I've seen many. Everywhere I've worked that uses a Scrum of Scrums, it has always been selected as a lightweight approach for teams to synchronize without putting a more robust scaling framework into place.
However, given the fact that the Daily Scrum is not a status meeting, but rather a chance for team members to synchronize and plan their day, I would treat the Scrum of Scrums the same, but at a broader scale. In the most successful Scrum of Scrums implementations I've been a part of, these were short, 15-minute meetings held every few days where representatives from the teams would synchronize on needs between teams and plan how to move forward together. The focus was usually how each team's work may be technically impacting other teams or what dependencies may be emerging or resolving.
As to who attends, the Scrum Master is rarely the best person to attend, since they are not one of the people doing the work. (Not that the Scrum Master can't attend, they just shouldn't be substituted for a dev team member) The approach I liked the most was actually that each team sent two representatives and those representatives rotated. But I've seen everything ranging from one consistent representative to even all team members attending.
Comment: Thank you very much for your valuable input. As you've mentioned, I suppose the aim of having scrum of scrums differs from organization to organization,
Answer: According to the Scrum@Scale guide it is more about sync and impediment removement:

The SoS holds a Scaled Daily Scrum (SDS). The SDS event mirrors the
  Daily Scrum in that it optimizes the collaboration and performance of
  the network of teams.
Read more in the Scrum@Scale Guide

Next it suggests a Scrum Master Cycle and a Product Owner Cycle, which would facilitate the organisational improvement cycles.
In this Scrum@Scale video Jeff Sutherland suggest (at 34:39) another responsibility of the Scrum of Scrums, namely: "Responsible for deployments of all teams together". So, it is also about keep delivering the product! Why have a meeting of Scrum Masters if they cannot deliver, faster and faster, that is their job, not?
Other scaling frameworks have a slightly different view, but I think it still focused on sync and impediment removal. This is how LeSS (Large-Scale Scrum) puts it:

A Scrum of Scrums meeting is a Daily-Scrum-like meeting between teams,
  typically held two or three times per week.
...
Scrum of Scrums isn't a part of LeSS and as a more formal centralized coordination technique, it is also not recommended. That said, if it is working, please don't stop doing it… yet don't feel you must do it because of adopting LeSS.
https://less.works/less/framework/coordination-and-integration.html
Comment: "Daily-Scrum-like meeting between teams, typically held two or three times per week"...@Niels I am genuinely smiling :-)  Maybe want to get less.works to update their documentation.

Scrum of Scrum of Scrums


What's the path to becoming a Posek

Question: What's the path to becoming a Jewish Orthodox Posek (like R' Yechiel Michel Epstein, a.k.a the Aruch Hashulchan). What Sefarim does one have to learn? What learning method is the most effective?
Comment: What do you mean by "posek"?
Comment: I revised my question. To make it more clear. @doubleAA
Comment: It's still not clear to me. What about R Epstein are you seeking to emulate? Using an ambiguous word and one ambiguous example isn't very specific
Comment: Studying Torah, Mishna, Gemara, Rishonim, Acharonim for a few dozen years will get you on your way. Then one needs apprenticeship with other great poskim. Then *siyata di'shmaya* (help from Heaven).Then maybe ...
Comment: DoubleAA is correct, there are people who know where answers are written and can quote from halachic texts. Then there are people who can generate new answers to difficult, often new, always grey-zone, questions. Those are typically people called *poskim*. The first could be called *talmidei chachamim*
Answer: According to the Gemara in Sanhedrin (5a), one would need to be learned (גמירנא), able to reason (סבירנא), and have permission from his (qualified) Rav (נקיטנא רשותא).  Normally, a rav will only grant this permission, known (colloquially) as סמיכה, semicha, after being satisfied that the student has proven the first two conditions, and possibly after an internship period known as שימוש (shimush).
There are several different areas of Rabbinic expertise.  For most religious questions (איסור והיתר), the permission is referred to as יורה יורה, "He may teach" (or decide).  For religious civil law, the permission is called ידין ידין, "He may judge" (or adjudicate).  Semicha may be limited to the scope of an individual's areas of knowledge (e.g. Shabbos, kashrus, Nidda) within the Shulchan Aruch.
There are many Kolels with semicha programs, and I believe Yeshiva University has one as well.  These programs generally focus on Orach Chaim, the laws of Shabbos and Yom Tov (sections 2 and 3, or 3 to 6 in the Mishna Berura), and on Yoreh Deah, the laws of kashrus (בשר בחלב and תערובות) and purity (Nidda and tevilla).  Other programs focus on civil law (in Choshen Mishpat) or on marital law (in Even HaEzer).  Those aiming for pulpits (or community rabbis) may have more specific requirements.
As for authoring a sefer, I would suggest that the question is a bit premature.  (Especially if you're asking on this site.)  However, the upper echelon of Poskim can generally issue rulings in all four sections of the Shulchan Aruch, and amass enough experience to gain acclaim among their colleagues others so they become the targets of queries (שאלות).  Eventually, an especially accomplished posek may have enough responses to be able to publish a sefer of שאלות ותשובות (Responsa).  Others may be able to write a commentary, or clarify a section of laws in their own words.  Aruch HaShulchan is of this latter form, and was written after Rabbi Epstein had been the rabbi of a large community for a number of years.

What's the path to becoming a Posek


How to determine heat exchanger equation?

Question: What is the equation to determine the inside surface temperature along the length of the counter flow heat exchanger?
Answer: The temperature equations for a counter flow exchanger are the same for a parallel flow exchanger as long as steady-state is a valid assumption, so the flow must be fully developed and the temperature profile must be fully developed. For a differential element where the flow travels along $x$ we have the conservation of heat.
Properties are known about substances and geometry and we analyze only the averages across the pipe's cross sections, $P$ is perimeter, $h$ is convection coefficient, $c_p$ fluid specific heat at average temperature, $T_m$ and constant (from steady state) average mass flow rate, $\dot{m}$.
$$Q_{in,pipe}+Q_{in,conv} = Q_{out}$$
$$\dot{m} c_p T_m(x) + h P dx (T_m(x) - T_s(x)) = \dot{m} c_p T_m(x+dx)$$
By the definition of the derivative and some algebra
$$\frac{\dot{m} c_p}{h P dx} \frac{dT_m(x)}{dx} + T_m(x) = T_s(x)$$
If you have the mean temperature profile of the fluid, then you can evaluate this expression. The mean temperature is often identified with the inlet and outlet temperatures and it may be the case that you will need a set of boundary conditions that describe heat transfer from surroundings into the pipe material and then into the fluid. While these may be closed form, they might be series solutions.


What does it mean when my influence level is "dominant"?

Question: So my influence level has passed "influential" and is now "dominant". I know "influential" over enough civilizations is enough to secure the cultural victory, but what does "dominant" mean?
Answer: According to this source, the tourism/culture levels are broken down like this:

"Exotic" (10%)
"Familiar" (30%)
"Popular" (60%)
"Influential" (100%+)
"Dominant" (200%)

Being "dominant" over another civilization affects public opinion and preferred ideology.  This means it is possible for other civilizations to conform to your ideology (if they are following another ideology) and impacts whether or not your ideology is "preferred".  Following a "preferred" ideology can greatly impact your civilization's happiness, so it should not be taken lightly!  Hope this helps!
EDIT:
Basically, influence levels dictate how much ideology pressure is applied to other civilization. Having a "dominant" influence would exert more ideological pressure to the other civilization. Besides that, there is really no difference between "influential" and "dominant" levels.
Answer: Dominant is the level of cultural influence above Influential, achieved at 200%. It doesn't contribute towards cultural victory but it does contribute to your influence over their ideology.
Being Influential over a civilization with a different ideology than you contributes towards the amount of unhappiness they receive from it. This can, in extreme cases, force them to change ideology or cause their cities to defect to you.
Answer: Dominant is basically the same as influential, you just exert at least twice as much influence over a civs ideology as you would if you were merely influential.


What is path of light in the accelerating elevator?

Question:
Mathematically, (by mathematically I means by equations) what is path of light in the accelerating elevator?
What is the difference between an ordinary derivative and covariant derivative (which is used in curved geodesic)?
Comment: You are asking two different questions here.. Perhaps you should create two different threads.
Answer: By the equivalence principle, the uniformly accelerated frame of the elevator than be treated as a spacetime with a uniform gravitional field.  The metric for a spacetime in which there is a uniform gravitational field in the $z$-direction is (with $c=1$)
$$
  ds^2 = -\left(1+ gz\right)^2dt^2 + dx^2 + dy^2 + dz^2
$$
Since this metric is invariant under translations in $t,x,y$, we immediately get three killing vectors $\partial_t, \partial_x, \partial_y$ and three corresponding conserved quantities along a geodesic $\gamma^\mu(\lambda) = (t(\lambda), x(\lambda), y(\lambda), z(\lambda))$;
\begin{align}
  c_t &= \dot \gamma \cdot \partial_t = -\left(1+ gz\right)^2 \dot t \\
  c_x &= \dot \gamma \cdot \partial_x = \dot x \\
  c_y &= \dot \gamma\cdot \partial_y = \dot y
\end{align}
where here overdots mean derivative with respect to affine parameter $\lambda$.  Light travels along null geodesics which satisfy $\dot \gamma^2 = 0$ which gives the equation
$$
  -\left(1+ gz\right)^2\dot t^2 + \dot x^2 + \dot y^2 + \dot z^2 = 0
$$
Combining these results gives
$$
  -\left(1+ gz\right)^{-2}c_t^2 + c_x^2+c_y^2+\dot z^2 = 0
$$
and therefore all in all we have
$$
  \ddot x = 0, \qquad \ddot y = 0, \qquad \ddot z = \frac{c_t^2g}{(1+g z)^3}
$$
If we choose $\dot t = 1$, so that the affine parameter corresponds to time, then we get the following
$$
  \ddot x = 0, \qquad \ddot y = 0, \qquad \ddot z = -\frac{g}{(1-g z)^3}
$$
In which case we see that the motion of light is such that it experiences no acceleration in the $x$ and $y$ directions and a position-dependent acceleration in the $z$-direction.  In fact, if we taylor expand the right hand side of the $z$ equation of motion with respect to the parameter $g$ then we find
$$
  \ddot z = -g + 3z g^2 + \mathcal O(g^3)
$$
So for small accelerations $g$, the light just experiences the acceleration of the elevator downward, plus higher order corrections.
Comment: How is that metric derived?
Comment: @AlexanderCska You should be able to use this as a jump off point to find one: https://en.wikipedia.org/wiki/Rindler_coordinates#Variants_of_transformation_formulas.  See also section 6.6 in *Gravitation* by Misner, Thorne, and Wheeler.
Answer: As long as you are asking about covariant derivative, I assume that you are interested in a relativistic treatment of the light trajectories. For this, a defenition of uniformly accelerating frame is needed. Take a look at Rindler coordinates. The article contains some information about geodesics, but it is hard to follow. The easiest way is to solve for geodesics in some inertial frame, where they are straight lines, and then pass to the accelerated system. I think that once I thought that they can be characterized as ellipses orthogonal to Rindler horizont, but I am not sure. You can google about Rindler Coodinates if Wiki is not enough.
As for the covariant derivative, the difference between a covariant derivative and an ordinary one is just some summ of Christoffel symbols :) Taken seriously -- the ordinary derivative just don't make any sense for non-scalar objects. General Relativity, and basically all Physics are not defined in a concrete coordinate system (here I mean that all theories are defined not by coordinates, but by some structures -- Riemann metric on a 4-manifold, Lorentz metric on a flat space-time, symplectic structre, a principal bundle, conformal structure, etc.). This means that components of your vectors should transform nicely under coordinate transformations. Ordinary derivative of a vector does not transform nicely, while the covariant does. Mathematically, ordinary derivative just cannot be defined without picking a specific coodinate system, while the covariant can. See the wiki article.


How to require stronger passwords?

Question: I am having a real hard time understanding why there is not a way to control the password strength of a front-end user registration form. With Craft 3, are there no settings anywhere to control this? I have a project that would include Craft Commerce to handle subscription payments, and during the subscribe portion, the user would need to register first. It seems so strange that a user can register with a weak password.
Answer: AFAIK, there's no current first-party policy enforcements, but there is this plugin we've used in the past to make sure passwords aren't easily guessed or previously pwned. I would give it a go in the meantime.
Comment: Thanks, I did look into this, but there was nothing in the documentation on how to implement it in the template or backend code. Is there a reference you can point me to?
Answer: You can also use front-end form validation to enforce stronger passwords than the Craft default, either with inbuilt browser functionality using the pattern attribute (more on that here) or JavaScript. It's not bulletproof by any means but it's an extra layer and it's the easiest way of implementing a stronger password policy for registering users.
I've used something like this in the past:
<input type="password" name="password" pattern="/^(?=.*?[a-zA-Z])(?=.*?[0-9])(?=.*?([^\w\s]|[_])).{10,}$/" required>

That regex enforces at least 10 characters, with at least one number and one symbol. You can tweak that to suit, but it helps ensure your user's passwords aren't particularly weak.
If you want to go further and create a more robust solution, you could create a simple module to listen to the beforeSave event for a User, and apply the same regex there in PHP as well. I realise that's a more involved solution and not all developers working with Craft are able and willing to create custom modules and dive into PHP, but I'm happy to throw a code example up if it helps.
Answer: You can add additional password complexity/requirement logic with a custom plugin/module by listening to the EVENT_BEFORE_VALIDATE on the User class.
There is an example of that for Craft 3 here: https://craftcms.stackexchange.com/a/12166/57

How to require stronger passwords?


how do i turn on group chat for my nokia 635

Question: My Nokia recently got restarted, and now when I try to send a group message it wont go through and says that I have to change my settings. I can't find where these text message/ group message settings are. Any help on how to turn group chat back on?
Answer: You can turn it on by going to the Messaging app, tapping on the three dots in the bottom right corner, then going to Settings > turn on group messaging. There's also more information on messaging here.


can't find executable installation file in droid explorer folder so how do I install on windows 10 please

Question: I am new to droid explorer, I wish to install it on my windows 10 system
I downloaded the software from this link https://github.com/camalot/droidexplorer.
I need a step by step guide on how to install the software itself as I can't find an executable installation file.
Thanks for your help in advance.
Answer: GitHub is mainly for developers, therefore the main view shows the source code repository. On GitHub the binary files are usually available in the "releases" section of each project.
https://github.com/camalot/droidexplorer/releases
In this page you can finde the ZIPed version of the DroidExplorer installer.


Recording a guitar, a Bass and one (or two) micro by scarlett 2i2 and Xenyx Q502USB

Question: If somebody can help to solve my question: I have a Scarlett 2i2 and a mixer Beheringer Xenyx Q502USB. Now I need to record a guitars, a bass and a microphone to the PC and I know that I can connect only one guitar to mixer. What if I connect the guitar and bass to the scarlett and the line outputs to the mixer line-in 2/3. The micro should be connected to the mixer to the xlr channel 1 and then by USB to the Mac. If possible I'll have both guitar and bass recorded in the same track I bealive and the micro in a different track. At the moment I have connected 2 audio monitors Eikon to the Scarlett output in order to listen the guitars.
Answer: It seems that the Behringer Xenyx USB mixers mix all tracks into one, so you won't have your microphone and guitars in separate tracks in your recording software (unless you record one track at a time).
There is a workaround (found here): pan one track to hard left and one track to hard right.  You will then get microphone in one channel and guitars in the other, which can then be split into two separate tracks after recording should you want to process them separately.  Of course that means you will only have mono recording, but that probably won't be an issue.
EDIT A further point - I've just realised that the Q502 actually has up to 5 inputs!  You don't need the Scarlett.  For smaller mixers with fewer inputs, the first diagram is valid.
Here are crude diagrams of the setups:
1) Using Scarlett
<code>                                Behringer
Microphone -------------------> Input 1------
                                Bal 100 % L  |
                                             |
                                             |---->USB to computer
                Scarlett                     |
Guitar-----------                            |
                 |------------> Input 2------
Bass  -----------               Bal 100 % R
</code>
2) Using multiple Behringer inputs
<code>                                Behringer
Microphone -------------------> Input 1 -----
                                Bal 100 % L  |
                                             |
                                             |
Guitar     -------------------> Input 2------|---->USB to computer
                                Bal 100 % R  |
                                             |
Bass       -------------------> Input 3 -----
                                Bal 100 % R
</code>
You are not able to map different channels on your mixer to different channels  on your recording software.  So the balances are a quick fix to separate the voice recording from the guitars when recording all of them at the same time.  You may have to 'split' L and R on your software after the recording.
Note that in all these cases the guitars will be irreversibly 'mixed', but you could record guitar and bass separately.
Comment: It seems that I can connect 2 instruments to Scarlett (of course) and 1 micro to the mixer. How have I to connect the Scarlett to the mixer and send the audio to the conputer togheter the voice ?
Comment: @Alessandro I've edited the answer, I hope that makes it clearer!


How did Alexander III of Macedon get the title "the Great"?

Question: Alexander III of Macedon is referred to as Alexander "the great", but who gave him this title? At what point in history was he acknowledged as such and why is he considered so great?
Comment: By taking names and kicking ass.
Comment: Conquering large chunks of territory will often get you some good press from historians. And dying young removes the arrows from their "Aw, he wasn't such a much" quiver. So - conquer much and die young. Rules to subjugate by. :-)
Answer: I think the first time he is mentioned as "Alexander the Great" (at least in the sources known to us) is Quintus Curtius Rufus' "Historiae Alexandri Magni Macedonis", this "Magni" has been translated into English as "Great". Here it clearly refers to his talent as a military leader which allowed him to build up a huge empire. Quintus Curtius Rufus was a Roman historian, this book is considered to be written in the 1st century AD.
Btw, Russian historians tended to focus on the word "Macedonis" which is why he is better known as Александр Македонский (Alexander of Macedon) in Russian.
Answer: Alexander apparently received that epithet from the Romans, who admired him. The oldest surviving reference of the title is found in the Mostellaria ("The Haunted House"), a play written by Titus Maccius Plautus (c. 254 – 184 BC). This roughly a century or so after Alexander's death in 323 BC.
Tranio:
Alexandrum magnum, atque Agathoclem, aiunt maxumas
Duo res gessisse. Quid mihi fiet tertio,
Qui solus facio facinora immortalia?`

- Mostellaria. III. 2. Titus Maccius Plautus.

Plautus seems to assume his audience would recognise who Alexandrum magnum was, an indication that the epithet may have predated his Mostellaria. It appears the Romans began styling Alexander as "the Great" shortly (relatively speaking) after his death.
The reasons are of course obvious, as @TomAu and @WladimirPalant have explained.

It took a long time before Alexander's greatness really came home to the Romans, although they were the people who, as far as we can tell, gave him the epithet 'the Great', and it took even longer before he made an impact on individual Romans. The earliest record we have of Alexander is in Plautus' Mostellaria, 775-7, where the slave Tranio brackets him with Agathocles, tyrant of Syracuse: Alexandrum magnum atque Agathoclem aiunt maxumas
 - Den Hengst, Danièel. Emperors and Historiography: Collected Essays on the Literature of the Roman Empire by Danièel Den Hengst. Vol. 319. Brill, 2010.
Answer: Alexander was called "the Great" by historians shortly after his death in his early 30s.
During his short life, we conquered essentially all of the modern Middle East and Egypt, starting with a base of Macedonia, a kingdom near Greece. In the process, he defeated much larger, mostly Persian armies, in an unbroken series of battlefield victories and successfully campaigns that are studied even to this day. Had he lived longer, he might have united large parts of Europe and Asia under Macedonian rule.
Despite his bellicosity, his rule was mainly benevolent. He treated conquered peoples kindly (relative to his time), and encouraged his Greeks to intermarry on equal terms with these people. Thus, Greek civilization spread throughout much of the Middle East with little further bloodshed. He also supported the development of learning, and his tutor, Aristotle, plus earlier scholars such as Socrates and Plato, were passed along to later generations as members the great minds of antiquity.
Comment: Sources for historians calling him "the Great" before Quintus Curtius Rufus?
Comment: @WladimirPalant While not "historians" per se, Plautus wrote of Alexander as "the Great" ~200 years before him.
Answer: Citations, while useful, are not allways necessary. Suffice it to observe that he did things no one achieved before, in scale, rapidity, modernity and efficiency:
 1. Created the largest sustainable empire by size as of then.
 2. Conquered and settled in lands never conquered before by the Greeks (the whole of Mesopotamia and the Persian Empire, Afghanistan).
2bis. Won even when outnumbered by a significant ratio.
 3. Waged war further than any other greek general (India).
 4. Ended the last native Pharaonic dynasty (to replace it by the dynasty of one of his generals: Ptolemy I Soter).
 5. Built or renamed at least 13 cities after his name (still named after him today: Kandahar (Afghanistan); Alexandria (Egypt))..
 6. All this before the age of 32.
 7. Was considered a local divinity in various parts of his empire.
 8. Never came back home, even for a day.
While sources of whether he really did that are necessary. Sources quoting him 'the Great' are pointless. If he did this, he was indeed great in many instances as compared with other mortals .


Why is 1-ethylidene-4-methylcyclohexane chiral?

Question:
As far as I can tell, there doesn't seem to be a chiral carbon in the compound, 1-ethylidene-4-methylcyclohexane. The C-4 of the cyclohexane ring has two groups with exactly the same connectivity, and the exocyclic double bond can't give rise to optical isomerism. What am I missing?
Comment: I'd say it's an interesting case of a compound with two stereoisomers, that are in the same time enantiomers (optical isomers) and "*cis/trans*" (*E/Z*) geometrical isomers.
Answer: The strict criterion for a compound to display chirality is that it must not be superimposable upon its mirror image. Let's ignore the chair conformation of the ring for a while, and assume it adopts a planar conformation. You could draw a side-on view of the ring like this:

We can see that if we reflect the molecule (in the plane of the ring + double bond), its mirror image is not superimposable on itself, which makes it chiral:

In practice, the cyclohexane ring does adopt a chair conformation. That does not fundamentally affect the fact that the compound is chiral, as the presence of a chair conformation cannot "remove" this existing source of chirality (for example, there is no way for the hydrogen and methyl groups to swap places by virtue of a cyclohexane ring flip or a similar process).
Actually, this is very similar to the case of an allene, which you may or may not be familiar with. Notice how the conformation drawn above looks almost like this allene:

with the planar ring taking the place of the second double bond. These are examples of axial chirality (Wikipedia; IUPAC), where the chirality stems from the disposition of groups about an axis (in both cases, the axis in question is the C=C bond axis). Further explanation of axial chirality in allenes can be found in this question.

A note on nomenclature
The tetrahedral chiral centre can be named with the usual (R) and (S) stereodescriptors, as described in user55119's answer.
When it comes to the double bond, ChemDraw (and likely some other software) suggest that they can be named with the familiar stereodescriptors (E) and (Z) (the process is also described in user55119's answer). However, this is not fully appropriate.

The exact rules are complicated, but it boils down to the fact that the double bond in question is enantiomorphic: that means that when it is reflected, the configuration of the double bond is reversed. We can see that from the names generated above: the two mirror images have supposedly different configurations at the C=C double bond.
The descriptors (E) and (Z) are supposed to be used only for diastereomorphic double bonds, where the configuration is invariant (i.e. does not change) upon reflection. The large majority of stereogenic double bonds fall into this category, but this one does not.
In place of (E) and (Z), the preferred descriptors are respectively seqTrans and seqCis (see mykhal's answer, and P-92.1.1 (f) of the 2013 IUPAC Blue Book) .
Comment: The analogy to an allene is a good one.  An equivalent description of a double bond views it as a two-membered ring (see [here](http://chemistry.stackexchange.com/questions/32407/why-can-there-not-be-more-than-one-sigma-bond-in-a-set-of-bonds/32522#32522) for example).  In the OP's molecule the two-membered ring has simply been replaced with a 6-membered ring.
Comment: In a sense, you do have a chiral center at the ring carbon opposite the double bond.  If you go around the ring in one direction you pass by the CH3 group at the far end of the double bond just before reaching the double bond itself.  Go around the other way and you pass a hydrogen atom at that point in the sequence instead.
Comment: @OscarLanzi You are right, and not just in a sense: that carbon is actually a proper chiral centre (this is reflected in the naming: it gets R/S configurations). I didn't spot it when I reread through.
Comment: @JoshMitchell [It's not particularly unusual](https://chemistry.stackexchange.com/help/self-answer), actually: I prepared the question and answer together. If you look through my profile you'll see I've done that on several occasions.
Comment: Did you ask this question 5 years ago and answer it yourself immediately after or something???
Answer: This question has been answered in elegant fashion by @orthocresol. I'd like to expand the discussion somewhat by detailing how digraphs and Cahn-Ingold-Prelog-(Helmchen) rules account for the ZR and ES assignments for 1-ethylidene-4-methylcyclohexane. To determine the configuration at C4, the double bond in ZR-1 is separated into two double bonds as a function of the pathway to C4. Digraph ZR-2 assigns the R-configuration to the chiral center (CH2CH2Z>CH2CH2E>CH3>H).
 To assign the geometry of the double bond (ZR-3), the double bond is kept intact and the methyl group is separated into two pathways to the double bond. The red dots terminating the two phantom chains are copies of the sp2 carbon of the double bond. Temporary Ro/So assignments are made with the phantom chains having the second highest priority. The double bond has the Z-configuration because Ro has priority over So and CH3 has higher priority than hydrogen.  The ES enantiomer can be analyzed in a similar fashion.
Answer: I would add that from the organic chemistry nomenclature standpoint, the double bond is enantiomorphic. In the current IUPAC Nomenclature of Organic chemistry, special stereodescriptors seqCis/seqTrans instead of Z/E are used in similar cases, here's an example

P-188.8.131.52.2.2 Specification of exo-cyclic double bonds by  stereodescriptors other than 'E' and 'Z'.
(…)
Example 2:

(1seqCis,3S)-1-(bromomethylidene)-3-propylcyclobutane (PIN)
  (3P)-1-(bromomethylidene)-3-propylcyclobutane

(Note: I think there is a typo in the latter M/P axial chirality stereodescriptor locant, should be 1, no 3)
So the preferred names of the two enantiomers are1

(1seqTrans,4S)-1-ethylidene-4-methylcyclohexane

(1seqCis,4R)-1-ethylidene-4-methylcyclohexane

(1) as provided by ACD ChemSketch 2018.1.1


What book on liberty did Lord Acton not write?

Question: Momigliano writes in his essay A Piedmontese View of the History of Ideas:

Lord Acton managed to become famous for a book on liberty he did not
  write.

What is meant by this puzzling sentence?
Answer: The quote refers to two things about Lord Acton.  First, he was anything but prolific as an author:

He is notorious for having rising to the heights of the historical
  profession without actually writing a book; the only work published in
  book form during his lifetime was his inaugural lecture when he became
  Regius professor of history at Cambridge.1

Second (and somewhat related to the first), he was obsessed with writing the definitive "history of liberty" but insisted on sourcing and researching it himself. The following makes use of a similar phrase, but puts it into a little more context:

The Cambridge historian Lord Acton (1834-1902) – who is best
  remembered for his maxim "Power tends to corrupt, and absolute power
  corrupts absolutely" – spent much of his professional life working on
  a single book, a comprehensive history of liberty. As one of the most
  knowledgeable historians of the nineteenth century, Acton was uniquely
  qualified for this ambitious project. Unfortunately, however, his
  rigorous standards of scholarship eventually got the better of him.
Distrustful of secondary accounts, Acton insisted on doing original
  research in every phase of his history. And since his history spanned
  over 2500 years, covered many different countries, and dealt with
  everything from the history of religion and philosophy to the history
  of political movements, it became virtually impossible for any one
  person, however brilliant and industrious, to complete the task that
  Acton had set for himself. Consequently, Acton's masterpiece was never
  finished, and his history of liberty, the work of a lifetime, became
  known as "the greatest book never written."

Much of the work he did on The History of Liberty has been published in various essays and collections, but his opus was never completed.
1 Boyd, Kelly. Encyclopedia of Historians and Historical Writing, Volume 1, p. 1
2 Smith, George H. Lord Acton and the History of Liberty, Part 1, online
Answer: The only hit I could find for misattributions involving Lord Acton is for a simple statement, not an entire book. This is what is sometimes today called Acton's Law: "Power corrupts. Absolute power corrupts absolutely".
Its true that isn't quite what he said. The full quote, from a letter he wrote to fellow historian Bishop Mandell Creighton in 1887 is:

Power tends to corrupt, and absolute power corrupts absolutely.

The popular phrasing only alters the sentence slightly, in the laudable interests of brevity and clarity. However, many argue that without the "tends to" it turns a statement about pressures into a assertion of an unstoppable mechanism.