CastAR bankruptcy claims documents - <AUTHOR> http://www.proofofclaims.com/castar/documents/ <comment><USER2> What a disappointment. CastAR was probably my favorite contestant for a VR/AR gadget.

And the reason is quite simple: I do flight and racing simulators. Anything involving a headset that occludes vision of your surroundings makes it impossible to see your controllers. It's fine as long as you're hands on wheel/yoke/stick and feet on pedals only driving or flying around with a relatively simple car or aircraft, but once you need to reach for the brake balance, landing gear, flaps, engine mode, air traffic control, pit strategy, etc, you need to find the right button. And there are plenty of buttons if you do serious sims.

CastAR would have been perfect for building sim pits because you could have a very large display area with the "relatively inexpensive" retroreflector fabric. I was dreaming about a simpit flight deck with aircraft window shaped reflective surfaces.

Oh well, I've managed so far with plain old monitors. Maybe will be a better gadget in the future, but none of the current VR gadgets do what I want.

</comment><comment><USER3> What actually happened here? They had working prototypes. The tech seemed sound, and not at all vaporware. Then it suddenly went quiet.

I always thought CastAR would be great for flight simulators with physical controls and instruments.

<comment><USER4> I was merely a Kickstarter backer of CastAR and have no insider knowledge, but my guess is that a failed moonshot attempt happened here.

After raising $1 million on Kickstarter, Technical Illusions/CastAR received an investment from Andy Rubin's Playground Global. CastAR later announced that they would refund Kickstarter backers' money and give everyone who backed at a level that would give them a pair of CastAR glasses a voucher for the retail CastAR glasses, whenever they released. Somewhere along the way, CastAR also changed course from "AR glasses tethered to a computer/phone" to "standalone AR glasses." Then they acquired Eat Sleep Play, a game studio in Salt Lake City. Then they went bankrupt.

Instead of releasing a product (even a rough, beta-quality product!) for their Kickstarter backers and iterating from there to a retail-quality product, it seems they took their VC money and went straight for a moonshot standalone product with first-party games available out of the gate. The moonshot was expensive, Playground Global declined to invest further, and here we are.

<comment><USER5> That sounds pretty plausible. I was deeply disappointed when they announced the pivot to standalone glasses. I didn't _want_ standalone glasses, I wanted the original device as pitched on Kickstarter. I figured, even if none of the VR/AR mechanisms worked at all, I'd have been thrilled to have a tiny set of display glasses with HDMI inputs.

As a backer, I'm pleased that they refunded everyone (and I can confirm having received a full refund). But I'm still sad to see this result; I had a lot of hopes for this, and it looked much more promising to me than any of the alternatives, right up until today.

</comment></comment></comment><comment><USER6> Glad they gave us backers our money back, but very sad and disappointing they didn't get the product out :*(

edit: Best of luck to all those involved. I'm hoping we haven't seen the last of Jeri and Rick.

<comment><USER7> I was a backer on "buy Jeri some coffee"-level. Too bad it didn't pan out but they tried.

At least we have a chance that Jeri might do a few new videos now.

<comment><USER8> >At least we have a chance that Jeri might do a few new videos now.

Silver lining indeed.

</comment></comment></comment><comment><USER9> Who are the major players still working on AR glasses? Meta and Hololens? Magic Leap?

<comment><USER10> Don't forget Daqri: [https://daqri.com/](https://daqri.com/)

Enterprise is the one vertical that's still pretty strong in VR/AR, perhaps because sky-high unit costs and dev investment can be amortized more easily.

</comment></comment><comment><USER11> thats sad. They had a really cool looking demo. Its too bad they couldn't at least deliver a v1 product to market.

</comment><comment><USER12> really unfortunate. its a pretty neat idea.</comment>


The Bodleian's 'secret trove of obscene material' - <AUTHOR> https://www.the-tls.co.uk/articles/public/sex-libris/ <comment><USER2> Sad to have missed the exhibition as a student of the University. My coursemates also found this quite amusing!

</comment><comment><USER3> Not so secret now.</comment>


Show HN: Invading privacy by inspecting localhost - <AUTHOR> https://github.com/wybiral/wtf <comment><USER2> Interesting finding. I am one of those people who thought localhost was 99.9% secure. Not a developer, tho. But did some fiddling in code. Thanks for sharing.</comment>


Ask HN: Looking for bulk image watermark tool for Mac? - <AUTHOR>

Does anyone know an app I can use to add a watermark in bulk to images? <comment><USER2> I'm pretty sure EasyBatchPhoto let's you do batch watermarking: <http://www.yellowmug.com/easybatchphoto/>

</comment><comment><USER3> Like obneq suggested, ImageMagick.

<http://www.imagemagick.org/Usage/annotating/>

</comment><comment><USER4> uhm, imageMagick? you might have to resort to using the terminal...</comment>


Show HN: Add a play button next to IPA on Wikipedia - <AUTHOR> https://chrome.google.com/webstore/detail/wikipedia-ipa-speaker/jkgihpigffcfeebgedpklldebdibbnne <comment><USER3> Kudos on a useful concept. Some feedback: Alternate pronunciations seems to go a bit wonky. For example it pronounces Ribosome [1] (/ˈraɪbəˌsoʊm, -boʊ-/) as ri-bo-some-bo :). Overall quite a nifty tool as many wikipedia pages do not have native pronunciation recordings. Could also see it helping casual learners of IPA.

_[1][https://en.wikipedia.org/wiki/Ribosome](https://en.wikipedia.org/wiki/Ribosome) _

<comment><USER4> You confused me quite a lot! Why did you "transliterate" /soʊm/ as "some"? Is there a dialect of English where "some" is pronounced as /soʊm/ and not as /sʌm/ or /səm/?

<comment><USER5> Likely "some" as in "home", not as the real English word "some"

<comment><USER3> Yes, that's exactly right. Sorry for the confusion lambdadmitry!

</comment></comment></comment></comment><comment> Null-Set This would make a good addition to mediawiki itself. Have you considered trying to contribute it to the project?

<comment><USER6> Agreed completely; this should be natively available in Wikipedia itself.

</comment></comment><comment><USER7> Ha! I Tried it with a couple names from my own language and it clearly is using an english TTS sound library. The pronounciation is better than you would get from a computer reading the name like an english word, but it's funny that even a language-neutral script such as IPA gets read with an english accent.

<comment><USER8> Accents can be (and many times are) specified in IPA scripts, so if the speaker carries an accent that isn't in the content he/she is reading or ignores any of the explicitly specified accents, then the pronunciation is wrong.

<comment><USER9> FWIW as well, linguists use different styles of IPA too, depending on the language families they most often work with.

Because of how it is used, IPA isn't really the 'one true standard' many would think it is.

<comment><USER10> That's the difference between a phonemic and phonetic transcription [0]. The former is bracketed with slashes (//), and the latter with square brackets ([]). To use Wikipedia's example:

Phonemic transcription of English "pot" is /pɔt/, and "spot" is /spɔt/. However, a phonetic transcription is closer to [pʰɔt̚] and [spɔt̚]. Note the addition of aspiration on the initial /p/ in "pot", and marking the /t/ as unreleased in both. But you don't need to differentiate stop aspiration in English, because they are conditioned allophones. And all final stops in English are unreleased, so you don't need to mark those phonemically either.

Basically, your first sentence is entirely correct, but your second sentence is a bit inappropriate. It serves it's purpose of a standard, but you must keep in mind that most transcriptions are not phonetic but phonemic. And a phonemic reading is not meant to be independent of the language -- there are plenty of languages for which [p] and [pʰ] are not allophones and must be distinguished in even a phonemic reading. You should be familiar with the phonemic conventions of a language in order to actually render a phonetic reading.

And even then, a phonetic reading will be dependent on things that boil down to individual speaker differences. That is, there is not any standardized, singular mapping of a phonemic transcription to a phonetic one, in _either_ direction.

[0] [https://en.wikipedia.org/wiki/Phoneme](https://en.wikipedia.org/wiki/Phoneme)

<comment><USER11> Something interesting I noticed here:

> Phonemic transcription of English "pot" is /pɔt/, and "spot" is /spɔt/.

Your use if this particular IPA indicates that you speak a dialect that has undergone the cot-caught merger, which probably means your accent is from Scotland, the western half of the US, or the Boston area. If you didn't, then you'd transcribe those words as /pɑt/ and /spɑt/ if you spoke a dialect with the father-bother merger (most American accents) or /pɒt/ and /spɒt/ if you spoke a dialect without it (many English accents, including RP).

I'm leaning towards you being Scottish, since Scottish English tends to merge them to [ɔ], while American dialects with the merger tend to merge them to [ɑ].

This goes to show that IPA transcriptions are heavily dependent on dialect.

<comment><USER10> I did transcribe it wrong; it's phonetically [ɒ] for me -- cot-caught is in effect.

Though this does give opportunity to point out that even phonemic transcriptions can have dialectal differences. There is no one phonemic transcription for English, as the different vowel mergers mean that minimal pairs differ between groups. This kind of variation tends not to happen as much with consonants as vowels, which make them much harder to transcribe even phonemically. But, for example, here's a list of mergers for non-rhotic dialects:

[https://en.wikipedia.org/wiki/Rhoticity_in_English#Mergers_c...](https://en.wikipedia.org/wiki/Rhoticity_in_English#Mergers_characteristic_of_non- rhotic_accents)

<comment><USER4> There is also a liiiiitle difference between RP's and SA's [i] and [ɪ] (IPA sounds are "areas", not "points"), as well as a difference in tenseness (British is generally more tense).

So yeah, IPA doesn't completely specify how things sound.

</comment></comment></comment></comment></comment></comment></comment><comment><USER12> How does this work? Where does the audio come from? Does it use some database of recorded IPA sounds, or does it convert from text to speech on the fly?

<comment><USER13> Judging from the source (viewable with Chrome extension source viewer [1]), it's POSTing the IPA text to [https://www.ipaaudio.click/audio](https://www.ipaaudio.click/audio) as the `ipa` key of a JSON object, the server does the heavy lifting and sends back an audio buffer, which the extension sends to a WebAudio context.

It'd be neat to know what exactly the server is doing, though.

[1]: [https://chrome.google.com/webstore/detail/chrome- extension-s...](https://chrome.google.com/webstore/detail/chrome-extension- source-v/jifpbeccnghkjeaalbbjmodiffmgedin)

</comment></comment><comment><USER14> It seems like once I push the play button I can no longer push the button again.

Console Error: ipa.js:38 Uncaught (in promise) DOMException: Cannot decode detached ArrayBuffer

Chrome 59.0.3071.115 (Official Build) (64-bit) Mac OS X

<comment><AUTHOR> Fixed. Thanks for your bug report!

</comment></comment><comment><USER15> Another great tool to anyone that likes Wikipedia, but hate to go back & forth between pages, or having multiple tabs all from Wikipedia.. I've developed this with a friend, and never got the time to distribute.. Free, made with love to UX and usability :) Enjoy _WikiLinks_ [https://chrome.google.com/webstore/detail/wikilinks/cdlabbcf...](https://chrome.google.com/webstore/detail/wikilinks/cdlabbcfbmmimjpcekcmoglnejgppncc)

<comment><USER16> Wikipedia is actually developing that natively currently as well: [https://www.mediawiki.org/wiki/Beta_Features/Hovercards](https://www.mediawiki.org/wiki/Beta_Features/Hovercards).

</comment></comment><comment><USER12> Is this add-on also available for Firefox?

<comment><USER17> +1

The idea is great but some more love for ffox users would be nice :)

<comment><USER12> I think the idea behind the new "WebExtensions" is precisely "write once - <USER2> everywhere". But I don't know if this add-on is one of them.

</comment></comment></comment><comment><USER18> IPA (international phonetic alphabet)

<comment><USER19> Thank you. My immediate trained response was India Pale Ale.

</comment></comment><comment><USER20> This is a great feature that has been missing for so long. Can't help but feel that IPA will go the way of cursive once tools like this propagate.

<comment><USER4> Adding to what Xophmeister said, IPA isn't just a notation, it's also a tool of thought. First, to efficiently quantize the stream of sound you need mental "buckets" to put the sounds to, and IPA provides your those buckets. Second, it may seem as if we hear "objectively", but in fact what you hear is very much affected by your language upbringing; for example, a ton of Americans can't really differentiate "pin" and "pen" even if the words are pronounced as in Standard American — they don't have a concept of the sound needed. IPA gives you those concepts.

<comment><USER21> That's a terrific way of putting it! Maybe we can say that IPA reminds of the challenges that are still out there for us in terms of distinctions that we overlook and sounds that we can't produce.

For example, I haven't learned to distinguish /pʰ/ and /p/ or /bʰ/ and /b/, as Hindi does, but thanks to IPA, I know that that issue exists and maybe I can learn it some day. Also, I haven't learned to say the consonant at the beginning of a Chinese friend's name (I think it's [ʈ͡ʂʰ]), and IPA helps remind me that [ts] and [tʃ] are just approximations to it.

<comment><USER4> Exactly! Moreover, even if I didn't learn the exact sound you are talking about, I can sort-of approximate it in my head. To be able to "transmit" sound in text is a proper super-power I would say, not too far from what Arrival pictured :)

</comment></comment></comment></comment><comment><USER22> more IPA speech synthesis

[https://eu-west-1.console.aws.amazon.com/polly/home/Synthesi...](https://eu- west-1.console.aws.amazon.com/polly/home/SynthesizeSpeech)

[http://speak-ipa.bearbin.net/](http://speak-ipa.bearbin.net/)

[http://developer.ivona.com/en/ttsresources/phonesets/phonese...](http://developer.ivona.com/en/ttsresources/phonesets/phoneset- en_us.html)

Also indirectly: [http://espeak.sf.net/](http://espeak.sf.net/)

</comment><comment><USER23> This is awesome! I can't tell you how many times I've clicked that link expecting it to take me to something more specific about pronouncing the word rather than just a generic page about IPA.

</comment><comment><USER24> Nice idea! I would also like a transliteration of IPA into pseudo-english (like francais = frahn-say). Most people don't know IPA well enough, and sometimes I don't want to or can't listen to audio. Also I find sometimes, having it written out helps with comprehension.

(While we are at it, can people please start "transliterating" names from languages that use the latin alphabet in very different ways, like "Saoirse (seersha)"? And liberally using hyphens to break up longer foreign words? I know everybody is proud and feels well educated when they can pronounce foreign names, but I think there is no shame in using pronunciation aids.)

<comment><USER25> Does "français" really sound like "frahn-say" to monolingual English speakers? It has always sounded more like "frahn-seh" to me, but that may be because I also speak Spanish. There's a recording of the word here: [https://en.wiktionary.org/wiki/Français](https://en.wiktionary.org/wiki/Français)

It's not an isolated example. For instance, "chez" is pronounced "shay" in English but in French it sounds more like "sheh" to me.

<comment><USER26> Are you making 'seh' rhyme with 'meh', or mostly with 'say', but saying it's subtly different? (If only there were some sort of phonetic alphabet eh...)

I would say it's most like the long 'a' in 'fate' or 'mate'.

<comment><USER25> I did mean rhyming with "meh", not a long "a" at all! In IPA, I'd say it's ɛ, like the vowel in the English word "bed".

So it really sounds like "a" to you? Huh.

<comment><USER26> Oh, interesting.

It does, yes, but as I alluded to that differs from 'ay' in which I'd linger slightly more on the end 'y' note if you see what I mean.

Less extreme than the way Americans linger on a syllable-ending 'r', but the same sort of thing.

</comment></comment></comment></comment></comment><comment><USER27> I see the button and it has mouseover text, but it's not actually clickable. Chrome Version 59.0.3071.115 (Official Build) (64-bit) on Windows 7.

<comment><AUTHOR> Ah! Nice find. I need css to make it a pointer. Will push a fix for that. You should be able to click the button anyway to hear the audio.

</comment></comment><comment><USER28> This is amazing, I have wanted something like this for over a decade. I check for something like this every few years. Thanks for making this!

</comment><comment><USER29> somewhat related: is there an extension that, upon mousing over hypertext linked to a wikipage, gives you a preview or summary of that wikipage? I feel like this would be incredibly useful.

</comment><comment><USER30> Would this work for Firefox, or does it rely on a Chrome-only TTS API?

<comment><AUTHOR> Should work fine in FF</comment></comment>


Ask HN: Roles as Endpoints or Scoped Roles for an API? - <AUTHOR> Hi, I'm creating an API and wanting some suggestions or feedback on how roles should be addressed. Currently the system has four roles (responder, dispatcher, regionaladmin, admin). They all have access to only specific portions of the API.
Example of Roles as Endpoints:
Responders can get events (assigned to them) but not post.

  GET  /v1/responders/events
 Dispatchers can get and post events

  GET  /v1/dispatchers/events
  POST /v1/dispatchers/events
 Example of Scoped Roles:

  GET  /v1/events
  POST /v1/events
 JSON Web Token with Scopes:

  Dispatcher
    {scopes: [events:read, events:create]}

  Responder
    {scopes: [events:read]}
 Which one of these would be better or more flexible? <comment><USER2> Design wise, I would definitely go with scopes. You would have one common API, just different requirements to make the calls.

OT: You got me curious how all this works under the hood now.</comment>


OpenSSL Security Advisory: TLS heartbeat read overrun - <AUTHOR> http://www.openssl.org/news/secadv_20140407.txt <comment><USER2> Ugh, that's a horrible vulnerability. We found something similar in nginx a few years ago, and the result is that you can repeatedly open up client connections and dump server memory as it changes, revealing keys and, without any real effort, authentication info and cookies.

<comment><USER3> not sure what you have to maintain, but it sure sucks having to scramble and fix this right away.

our (quick) fixes are almost all done:

\- recompile openssl where necessary (web, chat, mail, windows binaries) without heartbeat support

\- roll related certs and keys ASAP

and then comes the painful process of suggesting all web service users roll their certs and auth.

oh, and rotate personal passwords at other sites that issue a warning about openssl...

</comment></comment><comment><USER4> I had to google what "heartbeat extension" does:

       DTLS is designed to secure traffic running on top of unreliable
       transport protocols.  Usually such protocols have no session
       management.  The only mechanism available at the DTLS layer to figure
       out if a peer is still alive is performing a costly renegotiation.
       If the application uses unidirectional traffic there is no other way.

       TLS is based on reliable protocols but there is not necessarily a
       feature available to keep the connection alive without continuous
       data transfer.

       The Heartbeat Extension as described in this document overcomes these
       limitations.  The user can use the new HeartbeatRequest message which
       has to be answered by the peer with a HeartbeartResponse immediately.

[https://tools.ietf.org/html/draft-ietf-tls-dtls- heartbeat-01](https://tools.ietf.org/html/draft-ietf-tls-dtls-heartbeat-01)

Edit: here is the commit patching the bug [https://github.com/openssl/openssl/commit/7e840163c06c7692b7...](https://github.com/openssl/openssl/commit/7e840163c06c7692b796a93e3fa85a93136adbb2)

</comment><comment><USER5> "Don't roll your own parsers" should really be up there with "Don't roll your own crypto". This advisory is scant on details, but this extension protocol[0] neither looks complex nor beyond mechanical code generation to me. Just simple enough to be dangerous. And it's pretty new, so this must be recently authored vulnerable code.

[0] [http://tools.ietf.org/html/draft-ietf-tls-dtls- heartbeat-04](http://tools.ietf.org/html/draft-ietf-tls-dtls-heartbeat-04)

<comment> iso8859-1 Here's the commit for the fix: [http://git.openssl.org/gitweb/?p=openssl.git;a=commitdiff;h=...](http://git.openssl.org/gitweb/?p=openssl.git;a=commitdiff;h=96db9023b881d7cd9f379b0c154650d6c108e9a3)

<comment><USER6> Ouch, pretty basic lack of bounds checking.

Even though the code got better with this fix I still wouldn't accept code that looks like this in a review. Why are 1, 2, 3, 16 not defines? What's up with the code duplication between files? Where are the unit-tests?

I'm starting to feel that a lot of software that has been around for 10+ years and is commonly used does not live up to current best practices regarding writing good system-level software.

<comment><USER7> > I'm starting to feel that a lot of software that has been around for 10+ > years and is commonly used does not live up to current best practices > regarding writing good system-level software.

I get the impression that this applies to openssl far more than other software. The code base is a mess, _and_ it's security sensitive. So people dare not touch it.

It's a shame that there isn't a better incentive for this particular code base to be fixed.

</comment></comment></comment></comment><comment><USER8> "Heartbleed Bug" Q&A: [http://heartbleed.com/](http://heartbleed.com/)

<comment><USER9> Can we please vote this link higher? It's got a ton of information in it.

<comment><USER10> It's already at the top of the homepage, as a separate submission.

<comment><USER8> It is now. It wasn't at the time of vacri's post. Top of the homepage is best.

</comment></comment></comment></comment><comment><USER11> Ouch. Does this mean almost every Debian 7 web server out there is probably vulnerable to having its private data for supporting HTTPS compromised?

[https://security-tracker.debian.org/tracker/CVE-2014-0160](https://security- tracker.debian.org/tracker/CVE-2014-0160)

If so, that must be an awful lot of web servers, with a horrendous cost for everyone to buy new certificates etc. if there's no reliable way to determine what if anything was compromised.

Would any of our resident security experts like to suggest best practices under such circumstances?

(Edit: It looks like the page I linked above has been updated and a patch is going into Wheezy security as I write this.)

(Edit 2: Confirmed that Wheezy security updates now include openssl 1.0.1e-2+deb7u5 and related libssl changes.)

<comment><USER12> All reasonable certificate authorities will — at no cost — revoke your existing certificate and issue you a new certificate with the same expiration date as your old certificate. You'd just need to send the CA a new certificate signing request created from a newly-generated RSA key pair.

If your CA wants you to buy a new certificate to recover from a key compromise, your CA is taking you for a ride, and you should find a less horrible CA to throw your money at.

<comment><USER13> I think startssl requires $$$$ to revoke and/or reissue those "free" certs before they expire :-/

<comment><USER14> Is there another good CA that doesn't charge $$$ for both issuing and revocations?

<comment><USER13> I just got a revocation request accepted with no charge there.

</comment></comment></comment></comment></comment><comment><USER15> In case anyone was wondering why I wrote spiped...

<comment><USER16> Totally agreed on the over-complexity and un-securability of TLS, that too often is deployed where something simpler should be used instead.

However, wouldn't OpenSSH be the thing spiped replaces most of the times? And that has a better security track record (I mean, better than OpenSSL for sure).

<comment><USER15> A lot of people are doing spiped-like things using stunnel.

<comment><USER17> Basically, for internal infrastructure, where autossh wont work and/or where something simpler than ssh is desired.

So the strawmen arguments about it not replacing TLS is not the point.

stud, nginx, stunnel, f5 load balancers and cloudflare will still be needed for now, until 'moxie0 or someone comes up with a viable CA alternative AND something way, way simpler than TLS (brain-hurt ASN1, even with Wireshark).

</comment></comment></comment></comment><comment><USER18> Apparent introduction of the bug: [https://github.com/openssl/openssl/commit/bd6941cfaa31ee8a3f...](https://github.com/openssl/openssl/commit/bd6941cfaa31ee8a3f8661cb98227a5cbcc0f9f3)

</comment><comment><USER19> So they managed to notify Cloudflare in advance, but not debian/ubuntu security teams?

<comment><USER20> They may have had someone involved in the research / identification and fix.

</comment></comment><comment><USER21> Unfortunately, if you have been using an AWS ELB to terminate SSL traffic, they are vulnerable to this particular exploit. See this forum post: [https://forums.aws.amazon.com/thread.jspa?threadID=149690](https://forums.aws.amazon.com/thread.jspa?threadID=149690)

</comment><comment><USER22> Check for the extension:

        $ echo -e "quit\n" | openssl s_client -connect google.com:443 -tlsextdebug 2>&1| grep 'TLS server extension "heartbeat" (id=15), len=1'
        TLS server extension "heartbeat" (id=15), len=1

This doesn't tell you that the server uses OpenSSL, or that it is vulnerable, simply that it supports the extension.

<comment><USER4> I wrote a bash script to check the top 1000 websites and huge percentage of them responded with heartbeat extension (30-40%):

      INPUT=websites.csv
      OLDIFS=$IFS
      IFS=,
      [ ! -f $INPUT ] && { echo "$INPUT file not found"; exit 99; }
      while read rank website
      do
        echo "checking $website for heartbeat..."
        echo -e "quit\n" | /usr/local/bin/openssl s_client -connect $website:443 -tlsextdebug 2>&1| grep 'TLS server extension "heartbeat" (id=15), len=1'
      done < $INPUT
      IFS=$OLDIFS

You can download a list of top 1 million websites from Alexa and Quantcast: [http://www.seobook.com/download-alexa- top-1-000-000-websites...](http://www.seobook.com/download-alexa- top-1-000-000-websites-free)

Chinese websites timeout on port 443 so you'll have to skip them.

</comment></comment><comment><USER23> If your site is protected by CloudFlare (like HN is), you are automatically protected from this vulnerability (see: [http://blog.cloudflare.com/staying- ahead-of-openssl-vulnerab...](http://blog.cloudflare.com/staying-ahead-of- openssl-vulnerabilities)).

<comment><USER24> You are protected _now_. But you were not before, so if any attacker figured this out before the public disclosure then you have [possibly] already been attacked and compromised.

<comment><USER25> Not entirely correct, as the blog post states: > We fixed this vulnerability last week before it was made public.

Although there's still the other 103 weeks this was vulnerable to worry about.

</comment></comment></comment><comment><USER26> An Ubuntu update would be nice right about now. Outside of disabling everything that uses openssl or compiling a new one manually, there's not much I can do to secure my servers at this moment. Meanwhile, I'm guessing a lot of not so nice people are racing to scan IP ranges for this bug.

<comment><USER24> Debian already updated: [http://www.debian.org/security/2014/dsa-2896](http://www.debian.org/security/2014/dsa-2896)

Ubuntu should follow really soon, if not already.

Edit: Ubuntu updated: [http://www.ubuntu.com/usn/usn-2165-1/](http://www.ubuntu.com/usn/usn-2165-1/)

</comment></comment><comment><USER13> Are Android or iOS affected? Android seems to ship openssl 1.0.

Could a malicious server attack clients? Perhaps expose a browser's cookie jar or other saved passwords in memory?

The number of installed openssl clients across all devices and computers must be quite large.

<comment><USER27> Yes, the vulnerable code is used by both client and server so any client using openssl is affected.

<comment><USER28> Which parts of Android really use OpenSSL to do TLS with this heartbeat feature enabled?

The browsers? All Apps running on Dalvik? All apps running on ART?

</comment></comment></comment><comment><USER29> How does one go about installing this update on Ubuntu? "sudo apt-get upgrade openssl" didn't do it.

<comment><USER30> The fix has now been released by Ubuntu, so you can upgrade via the normal methods (apt-get update && apt-get upgrade)

<comment><USER31> Make sure you check running daemons too... apt-get install debian-goodies; checkrestart

</comment></comment></comment><comment><USER32> Is this something I have to worry about as someone who uses AWS ELB SSL offloading? Hard to tell from the docs.

<comment><USER33> Yes. [https://forums.aws.amazon.com/thread.jspa?threadID=149690](https://forums.aws.amazon.com/thread.jspa?threadID=149690)

<comment><USER34> Note that until it gets patched, you can go to your ELB config and disable TLS support, which I believe (someone please correct me if not) will protect you from this particular attack. Whether the cure is better than the disease is up to you.

<comment><USER35> Disabling TLS in the ELB config seemed to work for me until AWS finishes the patch rollout. (Looks like they're partway on the rollout.)

</comment></comment></comment></comment><comment><USER36> If one were using ASLR would this have mostly mitigated this? (I just rebuilt without the heartbeat extension but I'm curious). Also how exploitable is this?

<comment><USER37> I don't think ASLR helps here one single bit.

</comment></comment><comment><USER16> It should really be possible to easily detect what functionalities your deploy of OpenSSL is using and recompile only those.

</comment><comment><USER38> Anybody knows if the bug can be triggered in OpenSSH (I believe it uses the same lib?)

<comment><USER39> Most likely no since SSH is a different protocol than TLS.

</comment></comment><comment><USER40> Go C!

Hope everyone had forward secrecy on by now.

</comment><comment><USER41> I wonder how many service providers with big OpenSSL deployments (cloudflare, google, facebook, etc.) will do the sane thing and roll their authenticity keys. I'm guessing zero.

(Assuming they are deployed in such a way that their long-term authenticity keys are in the memory space of the network service, and not kept on another system or HSM.)

</comment><comment><USER17> If you'd like to update the keg-only OpenSSL brew on osx, and dont care for legacy and crap:

         ( export CONFIGURE_OPTS='no-hw no-rdrand \
           no-sctp no-md4 no-mdc2 no-rc4 no-fips no-engine'; \
      brew install https://gist.github.com/steakknife/8228264/raw/openssl.rb )

Beware, that by default on osx/ios, pretty much everything links to sketchy CommonCrypto or a crusty, quasi-deprecated 0.9.8.

<comment><USER42> of course, anyone using 0.9.8 is fine.</comment></comment>


Wharton professor: Google memo greatly exaggerates gender differences - <AUTHOR> https://www.linkedin.com/pulse/differences-between-men-women-vastly-exaggerated-adam-grant <comment><USER2> This article is arguing against four straw men. Damore's memo was not arguing that women have any less ability. Nor did it state that men and women are vastly different. It pointed out where statistically measurable differences exist.

It also acknowledges that culture does influence what careers women are interested in and offers some ideas on changing the culture in order to include more women. So Damore and this professor agree?

The memo was imperfect and jumped to conclusions many of which are probably incorrect, but I am really tired of it being mischaracterized.

This professor's piece is intentionally misleading.

<comment><AUTHOR> > It pointed out where statistically measurable differences exist. > So Damore > and this professor agree?

No, they don't agree. Grant is arguing that the statistics don't bear out Damore's argument that: "the distribution of preferences and abilities of men and women differ in part due to biological causes and that these differences may explain why we don't see equal representation of women in tech and leadership."

</comment></comment><comment><USER3> Excellent response to this by Scott Alexander: [http://slatestarcodex.com/2017/08/07/contra-grant-on- exagger...](http://slatestarcodex.com/2017/08/07/contra-grant-on-exaggerated- differences/)

</comment><comment><USER4> Hopefully this will stem the tide of "but muh freeze peach" sentiment on HN and elsewhere. Damore's views are not only wrong but harmful, and companies in the USA are entitled to terminate people who cause them harm, intentionally or not.

<comment><USER2> Technically Damore did not do the company wrong. He posted on a private, internal discussion board at Google. Someone else leaked it to Gawker, doing the actual harm to the company.

Also, his memo is concerned with what he believed potentially illegal practices at Google and so he may be protected by whistleblower laws.

Yes employment is at will in the US, however the legal analysis I've seen indicates he has above average chance of winning a suit against Google, if they don't just reach into their very deep pockets to settle out of court. He may walk away from this a millionaire.</comment></comment>


Models vs. Modules - <AUTHOR> http://www.37signals.com/svn/posts/1553-models-vs-modules <comment><USER2> Reminds me of... _Favour object composition over class inheritance_ , only we are talking about mixin inheritance instead of class inheritance.

</comment><comment><USER3> Summary: Object oriented beats monkey patching.

<comment><USER4> Actually, the two are orthogonal. You can monkey-patch an aggregation into a model as easily as you can monkey-patch anything else in.

Also, modules aren't monkey-patching. :)

      http://en.wikipedia.org/wiki/Monkey_patch

Lastly, the modules referred to in the article were added statically, not dynamically. We don't use a lot of dynamic module inclusion (though we do it some).

</comment></comment><comment><USER5> in django i separate model components into different files and then mixin in the relevant fields and methods. for example, suppose i define models Blog and Post in blog.py, and Rating and RatingMixin (extends object not base model). I'd give Rating a method, say Initialize, that gets called when importing the whole models folder. Rating.Initialize() would then mixin all the fields and methods in RatingMixin to the specified models. In this case, it might be useful to give Blog and Post the method "average_method".

Is this good practice?

Also, what's the advantage of keep lots of data in a single row versus multiple tables? Does it effect performance that much (esp with caching)?

</comment><comment><USER6> Simple question, why not have a db backed Avatar model instead?

<comment><USER4> It is db-backed. It's just that the fields exist on the people table, instead of in their own table.

<comment><USER6> Thanks, I never noticed model aggregation before. Looks really useful.</comment></comment></comment>


Ask HN: Is a Non-Compete Contract enforceable for a non-competitor? - <AUTHOR> Hello,  back in 2011 I signed a Non-Compete agreement with my employer (I was a doe eyed fresh graduate engineer).  I was given the contract on my first day at the job and had little choice but to sign it.
Now, I have accepted a job at a customer of my old employer.  The new employer does not compete or sell/offer services similar to the old employer (I do factory automation software, the new employer makes semiconductor chips).
My old employer seems to be pushing the angle that I am some how stealing business.  However, the customer will still be buying licenses from my old employer.  I will hire a lawyer in Portland Oregon to help (any recommendations?) if things get nasty.  But, does anybody have some experience? I am losing a ton of sleep.  Thank you <comment><USER2> I worked in online bookmaking where there is a massive amount of poaching. I would let your new employer know of this and let their legal team look after it for you (saves you the $ and the hassle.) That's what everyone who swapped companies in the industry did, was only an issue with upper management.

<comment><AUTHOR> I am just an engineer. My final title was "automation engineer". Not in upper management. Thank you.

<comment><USER2> Good luck! By an issue I meant the former company took them to court and was ordered to pay a few hundred grand

</comment></comment></comment><comment><USER3> Did you check if there was a term period for the Non Compete ? They should not be forever unless your employer tried to screw you. 2 years is the max I have seen for junior level employees.

<comment><AUTHOR> 5 years term. It also bars me from talking to customers that have expired 2 years before the end of my employment.

</comment></comment><comment><USER4> I'm not a lawyer, nor an expert in this but I have seen this happening. In my opinion it all comes down to what the non-competition clause states in the contract. I've seen cases where it was as broad as "in the automation domain" and also very specific like "in the domain of EDA tools development". In the first case the judge might not even consider the clause because it is clearly a treat to your freedom (you cannot do anything else). In the second case you are pretty much tied to it.

Be careful because if you were working for an EDA company the defense can state that the semiconductor company (customer) hired you to develop the same automation tools internally (potentially saving them money in the future), and that's competition.

PS: I have a friend who recently got hired on a direct competitor of our company (EDA x EDA). Apparently he (and his lawyer) proved to the judge that he is working in a project that is completely different from what my company does, so far so good for him. But since the clause only works for a definite period time (1 year), he can potentially change to do whatever he wants after this time. So it also depends on how good your lawyer is.... Also, the company that hired him knew of the issue and is supporting him with its own lawyers.

<comment><AUTHOR> This was very helpful information, thank you. I believe the new employer wants me because I have done a "lot" of phone support for them the past 2 years and have kept their plant running at the "wee hours" of the night on weekends. I have also done software extension work for them. The plant only has one automation engineer currently, and he really needs help managing everything.

Basically, if I can not do automation work for them they might not be interested in me.</comment></comment>


NY Attorney General targets fake social media activity - <AUTHOR> https://www.cnn.com/2019/01/30/tech/new-york-attorney-general-social-media/ <comment><USER2> haha you posted this 10 min after me. I deleted mine. You win this time. lol

Mine was literally under your posting.........</comment>


Ask HN: How do I build and grow human network? - <AUTHOR>

A bit of background and little rant. Apology in advance !
I am 29 and have little or no network at all. I know this may sound unbelievable but its true. I moved to US around 7 years back.
I have long forgotten people from school and college. Many were furious with me since I was really good in academics and maintained high ranks.
Then I joined small company where I could not make any long time friends. Only few people were known to me. But , not someone I could call for weekend fun trip.
I have been staying alone in US. My first job I worked on was big team but, again not so good people ( terrible hygiene, attitude and trying to get rid of always ! ) Current job , again not someone I could call and discuss idea occurred to me.
1. I am a bit shy. It is occurring to me I really don't know how to spark conversation ?
2. I don't know if physical appearance matter? I maintain very good hygiene, dress appropriately but I'm little fat.
3. I deleted facebook because if sad feeling it was creating ( I admit it ! )
I posted this question to reddit but someone always comments on read "How to win friends and influence people". I did that but that did not help.
I usually keep to myself , stay alone but I have really experienced downside of it. I really need to know and learn human connections and my human network. It may be little late but I believe in starting at some point.  I also understand that network is value proposition so I need to present something of value to have people in my network.
What are your thoughts, suggestions, books, IRL tricks, tactics to build and grow your network ?
I find many good advice on HN so any help is appreciated.
Keep rocking ! <comment><USER2> 1\. Where are you?

2\. Undelete facebook, don't read the news feed, let people add you and add people you meet and let them invite you to events.

3\. Find out what messaging programs people use (Skype, etc.), install them and keep in touch when possible.

4\. Go to meetups about things that interest you.

5\. Work on your english. Even better, if at all possible, go to language related meetups and get teach someone your first language in exchange for them improving your english.

6\. Lower your standards. When you don't know anyone you can't be super choosy. You can raise your standards after knowing more people.

</comment><comment><USER3> What are you good at, and what's your definition of fun? Once you've figured that out, go to Meetups related to those fields and you'll meet some people. Grow your network by meeting their friends, and so on. It requires patience and time, of course.</comment>


Dow plunges 1000 points - <AUTHOR> https://www.cnbc.com/2018/02/04/us-stocks-interest-rates-futures.html <comment><USER2> To put things in perspective: [https://en.wikipedia.org/wiki/List_of_largest_daily_changes_...](https://en.wikipedia.org/wiki/List_of_largest_daily_changes_in_the_Dow_Jones_Industrial_Average)

Saying "Biggest Point Drop in History" is a deliberate attention-grabber and incites more fear than it probably should. We should be more concerned with percentage changes and at -4.6% this doesn't even make the top 20 daily percentage drops, which cuts off at -6.98% for number 20 (see above link).

<comment><USER3> It looks like it might be in the top 100 though. Considering these are changes per _day_ , and the chart covers around 100 years or 25,000 trading days, this puts it in the top 0.4% of largest percentage daily losses. So, it does appear to be a significant losing day if 99.6% of such days are smaller in magnitude.

<comment><USER4> About 0.3% of days are my birthday.

<comment><USER5> Despite the downvotes, the point seems valid on its surface. We should expect a losing day this bad or worse more frequently than once per year, which doesn't sound that scary.

On the other hand, I wouldn't expect losing days to be evenly distributed (in the short to medium term at least) but rather clumped together.

</comment></comment></comment></comment><comment><USER6> Inflation finally is going up after years and we can get out of this stagnating economy. Wage growth up 3% in new January report and so we can finally expect interest rates to rise faster like they did in the past. Many investors, especially institutional ones have for years thought the stock market has been over priced but where else to park money because interest rates are too low?

Overall the 3% wage growth is huge for the economy especially because unemployment is so low. Other economic indicators also show a very healthy economy so when the next recession hits we'll have the tools to stop it. Inflation not rising has like stated baffled everyone so glad we are now dealing with what we know rather than wading into the unknown. The normal rules seem to apply again.

This is also why presidents shouldn't make their number one accomplishment the market because often times market crashes don't correlate with recessions or a poor economy. Trump did have a huge effect on the market, but not 10% which he thinks he did. That said the market is still higher than it was 5 weeks ago.

Risk averse savers will finally be rewarded. My biggest fear is the huge deficit, and the huge spending. I think the tax cut is great long term but could have been made significantly better, and could have scored under $100B deficit over 10 years under dynamic scoring (currently at 500B) if they decreased the top rate but still made it significantly higher than what it is today, and made the global min tax per individual countries but payable over time rather than all combined.

<comment><USER7> I wasn't a big fan of the tax cuts, even though I'll see the proceeds from them. Some think that the less you pay, the better, all the way to zero. In my view, taxes are like porridge, you don't want it too hot or too cold. The best amount is not too little or too much. I too worry about the deficit and think we need to tax the biggest gainers a bit more and provide safety nets for the economic losers so they can breath easy and participate in the economy a little more than just sustenance levels. As we've written and read about here in the past, it's expensive to to be poor (e.g. visiting the ER vs. early prevention, overdraft fees, etc). That may not be what you like to hear, but I also don't think we should tax the gainers too much either. There needs to be an incentive to to do well and I'd be against cutting into that too deeply.

<comment><USER8> I quite like your reasonable, balanced approach. I've always been curious about your last point though:

> There needs to be an incentive to to do well and I'd be against cutting into > that too deeply.

I've never understood why any tax rate would be a disincentive to do well. Even if the tax rate was 90%, doing well is doing well. If I make more money, I get to keep more money, even if taxes are high.

If we have tax brackets, then yeah sure there could be an unlucky minority of people who just barely land in a higher bracket than someone just under the line, so they pay a higher percentage than someone else.

But if you're well above the threshold, the amount you keep is more the more money you make before taxes. Isn't the _primary_ incentive at all times to make more money, regardless of taxes? Or is the idea of paying a higher percentage than someone else a strong enough motivator to actually keep people from trying? Or am I missing something?

<comment><USER7> As the tax rate increases, the value you get for increasing your income goes down proportionally.

I think if you take it to the limit, you can see the effect more clearly. As the tax rate approaches 100%, say 99%, then even if I make $100,000 before taxes, I'd only keep $1,000. If I push myself hard to earn $200,000, I'd get to keep $2,000. Yes it is still double, and I am doing better, but not much of interest changes in my life and I personally wouldn't say I'm doing well. I can barely afford to take that second vacation, or see much value for my efforts. My efforts are simply less rewarded, giving me less tangible reason to make the extra effort. I think this would kill off the incentive to create wealth in the economy.

Wealth is needed to take care of basic needs, so it would be self defeating if you were trying to take care of everyones needs and make sure they had a little spending money to participate in the economy.

Somewhat as an aside, I didn't consider what benefits I would receive for paying a 99% tax rate, presumably it would be all the basic needs plus some more, but this would start to feel like a planned economy where individuals, with their small discretionary funds, would't have as much input into what is created in the economy, rather it'd be a course political process which could be slow to meet the needs of the citizens, or fraught with other unforeseen difficulties.

<comment><USER8> Ah yes for the working class, I can see a 99% tax rate would very likely have this effect. I'm still wondering if we stayed in more realistic ranges, is a 40% tax rate, or even a very high 60% tax rate by US standards, a real disincentive to earning more money? I feel like it would take a pretty high tax rate before I stopped caring about my income. Does it actually have that effect in Norway, for example?

I realized I'm also mixing a few different thoughts in my head. I've heard the high taxes being an economic disincentive idea applied to the rich and to corporations and to investors, and I think my question applies more to them than to the middle class. You weren't talking about only the rich, I think I'm projecting a little bit.

Is the idea for businesses and investors that with higher taxes, in the aggregate there are always alternative places for the money, and so behavior changes statistically as tax rates increase? Maybe I'm interpreting "incentive" too literally.

<comment><USER9> > Ah yes for the working class, I can see a 99% tax rate would very likely > have this effect. I'm still wondering if we stayed in more realistic ranges, > is a 40% tax rate, or even a very high 60% tax rate by US standards, a real > disincentive to earning more money?

For me, and for people like me, it would be. I work high-paying shit jobs precisely because they pay a lot. The amount of saving I'm able to do in these jobs is life-changing (i.e. FU money after 5-8 years). If most of that money went to taxes, there'd be little point in doing them and I might as well induldge in doing something more satisfying instead.

</comment></comment></comment></comment></comment></comment><comment><USER10> I hate to be nitpicking about good news, but the S&P 500 is down less than 7% from it's peak, that's hardly a crash. Especially after gaining 26% over the previous year. And, after increasing over 90% the last 5 years.

Obviously, either way a decline in the stock market indexes is good news for almost everyone. I'm hoping for a real crash as I need to save lots more money, not just for my retirement but also for my kids college.

<comment><USER11> Not a crash, but the gains of January have just been wiped out in the few days of February trading.

<comment><USER12> If you're a normal person, not a day-trader, the time horizon your investments should be on the order of years, not months. If you're a day-trader, then this is just one of the risks of that choice.

<comment><USER13> If you're a normal person, who had a decently sized/exposed market retirement account in 2007, it took you about a decade to get back to the same level, inflation adjusted.

That's a lot of risk for chasing inflation adjusted returns…

Not to mention, there are a couple short volitilty ETFs that will be terminated soon, hope some long term ETF buyers won't be exposed to them or any big names they are holding who were exposed, because we're not done yet…

<comment><USER14> _If you 're a normal person, who had a decently sized/exposed market retirement account in 2007, it took you about a decade to get back to the same level, inflation adjusted._

Jesus! What was this average person invested in? From the bottom of the market to back to the prior peak was 3 years for me. And I was so heavy in equities I lost 1/3 of my portfolio's value.

Where does this "decade" come from? The DJIA is nearly 90% higher than the peak pre-2008.

And I know you said inflation, but that has been 1-2% per year since then.

<comment><USER13> I had in mind the ^RUA, which only started to break out from the previous top after 5 years, nominally, so you're right, not a decade, but not good for someone trying to retire within that time frame (which doesn't seem like you were).

Still, I worked for a fund that swing traded futures for better returns and less risk than holding the market during this period…

</comment></comment></comment></comment></comment></comment><comment><USER15> I was just reading:

[https://static1.squarespace.com/static/5581f17ee4b01f59c2b15...](https://static1.squarespace.com/static/5581f17ee4b01f59c2b1513a/t/59ea16dbbe42d6ff1cae589f/1508513505640/Artemis_Volatility+and+the+Alchemy+of+Risk_2017.pdf)

tldr; * The Global Short Volatility trade now represents an estimated $2+ trillion in financial engineering strategies that simultaneously exert influence over, and are influenced by, stock market volatility

* Since 2009 Global Central Banks have pumped in $15 trillion in stimulus creating an imbalance in the investment demand for and supply of quality assets

* Last month Austria issued a 100-year bond with a coupon of only 2.1%(6) that will lose close to half its value if interest rates rise 1% or more.

* Amid this mania for investment, the stock market has begun self-cannibalizing... literally. Since 2009, US companies have spent a record $3.8 trillion on share buy-backs financed by historic levels of debt issuance.

* Every decline in markets is aggressively bought by the market itself, further lowing volatility.

* Volatility is now at multi-generational lows... Volatility is now the only undervalued asset class in the world. Equity and fixed income volatility are now at the lowest levels in financial history.

<comment><USER4> How is Volatility an asset, and how does one take advantage of this?

<comment> d--b Banks sell derivatives indexed on vol, like vol swaps and var swaps.

VIX futures also reflect stock market volatility, and their prices are based on S&P option prices.

<comment><USER4> Ah VIX - I saw that [https://news.ycombinator.com/item?id=16313832](https://news.ycombinator.com/item?id=16313832)

</comment></comment></comment></comment><comment><USER16> Cripes, it's plunged to levels only last seen 2 whole months ago.

</comment><comment><USER17> I would not have worried too much of a Dow correction, but I feel like a trifecta of events are coming together that is a bit concerning. First, is the explosion of US government deficit which could potentially lead to austerity measures in the near future. Second is the threat of inflation and overheating. And third is the plunging savings rate of individuals. It almost appears that these three are moving to a confluence. Austerity + rise in interest rates + depleted savings could lead to a consumer spending crash in the near future.

<comment><USER14> Plunging saving rates? Saving rates jumped after the last crash. They are far higher in the US than countries like Canada, for example.

<comment><USER17> US savings rate actually dropped to a 12 yr low recently [https://www.marketwatch.com/story/why-the-savings-rate- falli...](https://www.marketwatch.com/story/why-the-savings-rate-falling- to-a-12-year-low-is-not-a-death-knell-for-the-us- economy-2018-01-29?mg=prod/accounts-mw)

<comment><USER14> Thanks for sharing that.

Considering the noise in that chart (savings rate drops from 11% to 5% in one month?!?), I would question whether it's really a trend and how accurate the data is.

One of my pet peeves with economic data - some leading indicator plummets after being high for years. Mass panic in news headlines, only for it to return to normal the next month.

</comment></comment></comment></comment><comment><USER18> part of my biggest sell indication was a visit to the site zerohedge. They are a very bearish - gold centric site. I like to visit sites like these to balance out the generally optimistic news one sees elsewhere. Recently, I have noticed that the site has lost their commenters - they are all making fun of the site and how it cost them so much money, missing out on all these gains. I realized that completely aside from things like inflation upticking, the fed removing some QE, market being incredibly highly valued - that if one of the largest bear sites around had actually lost their crowd, that even that rank and file thought it was stupid to doubt that the DOW would only go up...it might be time to think about taking a step back. At least until post-Brexit next year.

</comment><comment><USER19> The specter of rising interest rates in the US (driven by higher inflation expectations) appears to be a factor.[a]

Fast-growing companies that are investing aggressively today and whose profits lie far in the future, in particular, are exposed to rising interest rates, due to the higher _duration_ of such companies' cash flows.

Duration, for those here who don't know, is a measure of the sensitivity of present value to interest rates.[b] Duration rises with the amount of time an investor must wait for cash flows, and vice versa.

For example, the present value of $100 of cash flow in 10 years, if the 10-year rate is 2%, is equal to $100/(1.02^10) = $82; if the 10-year rate rises, say, from 2% to 3%, the present value declines to $100/(1.03^10) = $74, or a _-10% decline_. However, if the $100 in cash flow is in 30 years, and the 30-year rate rises from 2% to 3%, the present value declines from $100/(1.02^30) = $55 to $100/(1.03^30) = $41, or a _-25% decline_.

In this example, an increase in duration from 10 to 30 years caused the sensitivity of present value to a 1% rise in interest rates to change from a -10% decline to a -25% decline. The longer an investor has to wait for cash flows, the greater the sensitivity of present value to changes in interest rates.

The same ruthless logic applies to companies. The present value of companies whose profitability is in a distant future _declines much faster_ when interest rates rise than the present value of companies certain to generate cash flows in the near future.

Until recently, due to historically low interest rates and no prospects for inflation, the stock market has been rewarding high-investment companies that are sacrificing current profits for growth.

If interest rates continue to rise (along with expected inflation), I'd expect this abruptly to change -- in which case, strap on your seat belts!

[a] [https://www.ft.com/content/af1f8e4a-0a23-11e8-8eb7-42f857ea9...](https://www.ft.com/content/af1f8e4a-0a23-11e8-8eb7-42f857ea9f09)

[b] [https://www.investopedia.com/terms/d/duration.asp](https://www.investopedia.com/terms/d/duration.asp)

</comment><comment><USER20> A market is like a forest and a market crash is like a forest fire. In order for the market to grow and be healthy in the long term, a purge every now and then is necessary.

<comment><USER21> Last time round (2008) we deferred the purge, when you do that the next forest fire is potentially even bigger.

</comment></comment><comment><USER22> For most HN readers this means you should be buying more stock.

<comment><USER23> Right.

Better yet, wait for the end of this correction, _then_ buy more stock.

Better still, sell any stock you own, and at the end of this correction, buy it all back and more at a cheaper price. Yeah, that's the ticket!

Guys, all we need to do is find out when this correction is going to end. I feel like we can narrow it down to between one day and one year from now.

<comment><USER24> >> wait for the end of this correction

How exactly do you decide the end of it has been reached?

<comment><USER25> Whatever money I'd put in right now, I'd diversify the time component. Instead of buying 1x at once today, tomorrow, buy 0.2x every two/three days.

</comment></comment></comment></comment><comment><USER26> The dollar has weakened over the past year, so knock off 1/4 point off any quarterly GDP numbers proposed, and knock 10 points off the 23% the 401(k) supposedly got in the past year, and consider any inflation comes with assymetric timing risk where wages always lag by a lot. And now in real terms the past year's stock increases look a lot more ordinary rather than remarkable. It's not like the stock market is going to ignore a weakening dollar, in particular when the Treasury Secretary publicly says it's a good thing as if it's an actual policy to have a weak dollar.

And working people have to feel the sting of inflation before they demand wage increases, they don't just automatically happen. Before that, interest rates going up might increase housing sales as people want to get "in" before the interest rates go up even more, and then housing will slowly taper off as inflation and interest rates take hold, and people get priced out of buying, since their wages will not keep up in the short term.

Inflation also helps pump up tax revenue, and monetize debts. So the numbers will look better, but in real terms they won't be better for a while until the markets fully correct for inflation and then things stabilize a bit.

</comment><comment><USER27> "Fruits of capitalism available at a 3.5% discount to last month; limited time offer" would sell less ads, sadly.

</comment><comment><USER28> Biggest by absolute value or by percent?

<comment><USER29> It's a great question, because point drops are not a very useful metric.

<comment><USER30> Yeah i expect this record to be shattered multiple times in my lifetime.

<comment><USER31> I _hope_ [this point record] is shattered many times.

Otherwise, I've died young or the market hasn't grown much over my remaining ~40 years of life...

</comment></comment></comment></comment><comment><USER32> What's with the 600 pt 3pm sell-off and recovery within 5 minutes? Algorithms? I thought massive swing effects are supposed to be under control now?

<comment><USER33> > are supposed to be under control now

Why would you think that? Massive swing effects are often caused or exacerbated by algorithms trading on momentum.

They do that because trading on momentum usually pays, and doing the hard work of fundamental value investing is difficult and also hard to scale.

Momentum trading is fine if only a few people are doing it, but if enough of the market transitions to having 'no opinion except following the crowd', then you get instability just like this. And many factors since 2010 have made flash crash-like events easier to cause, not harder.

<comment><USER34> Unlikely. Momentum works terribly for equities, doubt there are many people doing it.

</comment></comment></comment><comment><USER35> Think this is relevant here...

[https://www.npr.org/sections/money/2017/01/04/508261371/epis...](https://www.npr.org/sections/money/2017/01/04/508261371/episode-443-dont- believe-the-hype)

</comment><comment><USER36> Just by looking at the continuously negative % drop over the historical data, there's a pattern in 2008 (The Crash)

9/15/08 9/29/08 10/7/08 10/9/08 10/15/08 10/22/08 12/1/08 −4.42 −6.98 −5.11 −7.33 −7.87 −5.69 −7.70

8/4/11 8/8/11 8/10/11 −4.31 −5.55 −4.62

8/21/15 8/24/15 −3.12 −3.57

2/2/18 2/5/18 −2.54 −4.60

For 2018 to reach 2008 state, lets see if there are more significant (>-4%) drops in 2018 for us to start freaking out.

Again this by all means is not a financial model, it is something that I put together to tell myself "Keep Calm"

</comment><comment><USER37> Market crashes don't necessarily have to result in economic pain. But when they did, both in 2008 and 1929, it was because the rise in stock prices was financed by debt. I'm worried that that might be the case today in the form of leveraged buybacks and the like, but I can't find any statistics on how much of the current asset bubble was debt financed. I suppose we'll know soon enough.

</comment><comment><USER38> It's grim to see how unprepared websites are for sudden activity like this. I'm having a tough time logging in to my accounts.

<comment><USER39> On the bright side, at least sysadmins are first in line for a bank run.

</comment></comment><comment><USER40> I do worry that this is the end of the current bull market and we'll be entered into a recession in the next half year or so.

<comment><USER29> Stock market corrections do not always lead to or cause a recession (or vice versa). Many Americans do not even own stocks, so something like today will be a passing news item barely noticed.

If you think a recession is coming, what will be the trigger(s)? Right now companies are making money, wages are finally growing, and jobless claims are near what some would say is full employment. The only real euphoria I see is in crypto, and I just don't see a problem there being able to spread economy wide like what happened in housing.

<comment><USER41> >If you think a recession is coming, what will be the trigger(s)?

Not in the immediate timeframe, but there are some potential breakers looming out there that have potential to hit in the next year or three.

The first is inflation, and the fact that we just pulled a massive tax cut. This will probably lead to stock buybacks, throwing gasoline onto the already booming economy. Usually it's best to save the cuts for busts, to stimulate growth. Now it's like throwing that third fuel pack into the train engine on _Back to the Future III_.

The second is the education bubble. The wealth gap is slowly but steadily growing for the current generation, and student loans are a strong cause. This is more insidious because you're turning out a generation with decreased buying power that they won't recover from without intervention. Depending on the method of the intervention, it could lead to debt disappearing which will cause another recession.

Lastly is the housing bubble. It busted in some areas but is still booming in others, thanks to no financial reform to prevent it from happening again. This alone won't be a large enough factor to trigger another recession, but could when combined with another smaller cause, like inflation. The fed has moved up the interest rate increase schedule because it's becoming obvious that we're looking at signals pointing to increases in inflation.

<comment><USER42> I recall hearing about a subprime auto loan bubble too.

</comment></comment></comment></comment><comment><USER43> Let's say you're a smart investor, and you think a big crash is coming. Right now everything you have is in stocks.

What do you move it to to hedge your risk?\\\

Edit: To clarify, I don't have everything in stocks. I'm just looking for good advice on how to further diversify. I'm aware that timing the market is a fool's errand. :)

<comment><USER44> A smart investor will always have a set of numbers in mind - say 60% stocks and 40% bonds - and every 6 months will rebalance the portfolio to that.

Over decades this will return better returns at dramatically less stress than any other approach.

<comment><USER45> I'm sure there's some dimensions it's not optimal on, but Vanguard LifeStrategy is a single low fee fund that does this for you. IIRC they have 20/40/60/80/100% equity options.

<comment><USER46> Here's my own anecdote ...

After hearing so many people say positive things about Vanguard for so long, I set up an account there. They had pretty much all my disposable cash, in a Roth IRA, for about two years. Rather than begin the predictable uptick in wealth I expected, my results, having about $25K parked there, was that I lost about 300 bucks. I sent several messages asking what I could do about it, their responses were gobbledygook that I did not understand, so I took all my money back out. Praying that I don't wind up with a huge tax burden this year, due to this mistake.

Here's my message: regardless of the hype, Vanguard is not for unsophisticated investors. I am looking for an actual human being who can help me invest, now.

<comment><USER47> What did you invest in? If a 1.2% swing (over how long of a period?) spooked you then you probably want a heavy bond to equity fund/balance.

<comment><USER46> see, those are the exact sort of questions, and answers, that you are prepared to provide. and you're probably pretty good at it! i am not. that's why vanguard didn't work for me.

i am going to pay an actual human being to give me a list of options, with all the pros and cons spelled out, so i can make limited decisions that wind up with my pile of money growing, instead of shrinking. if that's too much to ask, i'll just keep my money under a mattress, thanks.

<comment><USER47> > see, those are the exact sort of questions, and answers, that you are > prepared to provide. and you're probably pretty good at it!

Thank you, but it really has been a recent thing for me. It's only in the past year that I actually worked out what this all means, passive versus active investments, pensions etc.

> i am going to pay an actual human being to give me a list of options

I totally understand that but do me a favour. Before you pay anyone or start down that route, watch this playlist - [https://www.youtube.com/watch?v=_chiIIxMGl0&list=PLXy71rkGuC...](https://www.youtube.com/watch?v=_chiIIxMGl0&list=PLXy71rkGuCjXLg9N8zowwUpXCYfBcMJFK)

It was accidentally stumbling across that which led to me getting my stuff together. At the very least it should give you a grounding in what to read up so as not to be blindsighted by any financial advice you may get in the future from a professional.

> instead of shrinking. if that's too much to ask, i'll just keep my money > under a mattress, thanks.

Inflation is always eating away at your money there, no matter how thick your mattress is ;)

<comment><USER46> > Inflation is always eating away at your money there, no matter how thick > your mattress is ;)

while that's true, if i'd kept my money under a mattress for the last two years, i'd have 300 bucks more than i have now. and with a lot less hassle.

so, here's another story. i hate paperwork. hate, hate, _hate_. i hate it enough that i pay a guy to do my taxes. i send him the forms as they trickle in, sign what he tells me to sign. he answers my dumb questions about my mortgage and my car loan and other financial stuff, when i ask them. i give him a check for like 200 bucks a year, and i consider it money well spent.

i've been working with this guy for over ten years now. he's proven himself to be absolutely trustworthy. i tried to give him even more money to manage my portfolio, but he is not interested in having that job, so he turned me down.

is it really impossible to find somebody like him, to be my money manager? while i hate paperwork, i am a really good judge of character. i dispensed with half a dozen shysters before i landed on my current guy. i could do the same thing with financial planners.

</comment></comment></comment></comment></comment></comment></comment></comment><comment><USER48> It's also just coming off an all-time high. The worst performer this session was the index's top performer in the run-up, which strongly suggests this drop was fueled by profit taking. One thing to realize is that the market sometimes just moves because of traders trading...

</comment><comment><USER49> This is also the first downward correction after a 59 year record month over month gain run of 10 consecutive up months. It's also been about 9 years since the last true recession so I'd say the alarmism in the headlines is warranted.

</comment><comment><USER50> Interesting to see the volatility in all these market these days.

I wonder how much the spread of information/social media plays a role in this. it does seem like most of these swings seem to be from retail investors.

<comment><USER51> Interesting that VIX has been at an all time low for the last year or more. So volatility has been at an all time low. These last few days have been rough, though.

<comment><USER52> VIX attempts to measure volatility but it is not volatility itself. The lowness of VIX has been driven by the relative increase of the denominator (total asset value, which has surged in the last few years) not by a decrease of the numerator.

In general, it's usefulness as an indicator of volatility has decreased lately.

<comment><USER53> VIX measures the risk premium on options on the S&P 500 index. I don't see how total asset value ends up in the denominator?

Another explanation is that VIX is being actively dampened by the growing popularity of the 'short volatility' trade. E.g., the SVXY ETF among others. We're seeing today just how volatile volatility can be!

</comment></comment></comment></comment><comment><USER54> Once again, Dow is an awful indicator even without the awful usage of absolute numbers when numbers are obviously higher now.

Now the reason for my post. Where should I go for non-sensational finance news?

</comment><comment><USER55> Surprised no one has made the cryptocurrency equivalent of VIX that moves in the opposite direction of a basket of cryptocurrencies.

<comment><USER56> Short Overstock. It moves very closely in align with crypto.

<comment><USER57> Why is that? Do they have exposure to crypto?

<comment><USER58> Yeah, they've made it a point to emphasize that they're working on crypto / bitcoin related things[1].

1: [https://www.investopedia.com/news/overstock-goes-all- bitcoin...](https://www.investopedia.com/news/overstock-goes-all-bitcoin- stock-climbs-300-2017/)

</comment></comment></comment></comment><comment><USER59> Also, Programmed trading, excitement in the run up = more people buying, more greed = more use of margins = more margin calls.

</comment><comment><USER60> At one point down -1,600. I did a little buying today (BRK.B), this was margin calls, algo trading, and fear.

<comment><USER61> It's certainly a good idea to buy when stocks are undervalued. However at the moment they are likely still overvalued, and it's also quite early days in this current sell-off.

I just sold my entire portfolio (apart from retirement funds) earlier this morning, as we want to buy a house later in the year and don't want to get trapped if the stock market completely crashes.

<comment><USER62> I've been watching for a sell signal for about 6 months, and I also got (mostly) out this morning.

<comment><USER14> The chance of you actually timing getting back into the market at the right point is really low. Miss the best days of a run up and you're giving up 75%+ of your returns.

Far better to hold steady.

<comment><USER62> It's been 10 years. Pretty epic bull run. I'll cross the re-entry bridge at a later date.

</comment></comment></comment></comment></comment><comment><USER63> Yield curve isn't negative yet. I'd wait until that happens before calling it a bear market.

</comment><comment><USER64> DOW != economy

A stock crash is not a recession. The stock market is not the economy. Stocks falling is not a recession.

<comment><USER65> OTOH, stock market crashes are not uncorrelated with recessions.

<comment><USER64> There are actually a lot of examples where this is not true

1987 stock crash? No recession.

1980-82 recession? No stock crash.

1992 recession? Also no stock crash.

<comment><USER37> A stock market crash only leads to recession if the preceding bubble was financed with debt. Which, sadly, might be the case this time due to leveraged buyouts and buybacks. In 2008, the housing bubble was financed with easy credit. In 1929, the stocks were all bought on the margin. Then it's really painful to unwind the bubble. If that is the case this time around, we'll know when all those companies that bought their own shares back at inflated prices go bankrupt at the same time.

</comment></comment></comment></comment><comment><USER66> it's simple...

Higher than Expected Inflation = Faster than expected Rising Interest Rates = Cuts in Growth Outlook = Stocks go Down

</comment><comment><USER67> Don't stress about this correction. No matter what happens, when it's over we'll get right back to making _real money_.

</comment><comment><USER68> But why hasn't it happened already?

</comment><comment><USER69> Call me old fashioned but it's a nice change of pace to see news about traditional market indexes crashing rather just crypto currencies.

<comment><USER70> Different reasons. I suspect this is due to traders taking their yearly profits and then stampede set in.

The volatility index has a very sudden spike at the end of the market

[https://finance.yahoo.com/chart/%5EVIX/](https://finance.yahoo.com/chart/%5EVIX/)

<comment><USER11> > I suspect this is due to traders taking their yearly profits

Thought that happened in December, not February. A short year for traders this year, I guess.

(unintentional pun)

<comment><USER71> Nope, Nov through January are historically great months for stocks with February usually being one of the worst. One cause of this may be fiscal tax years not necessarily aligning with calendar tax years.

Edit: One of the more interesting and notable causes is that many fund managers and investment advisors will actually rebalance portfolios so that at years end it appears they were holding the biggest winner stocks/assets. Basically a marketing trick.

</comment></comment></comment></comment><comment><USER72> Unprecedented growth leads to unprecedented correction. This is profit booking but huge players. The market will stabilize and start rising again. The fundamentals are still strong

<comment><USER73> Have you looked at the extreme bubble valuations that are essentially everywhere in the market? The fundamentals are horrific.

2.x% GDP growth stacked against peak PE ratios like ~40 by Coca Cola (KO), with zero (or negative) growth for years.

Who are the crazy investors paying that? The US and global economy can't expand fast enough to pull down these multiples in a reasonable amount of time.

50 times earnings for PayPal, for astounding 15% style growth. And similar for Netflix, except at 200 times earnings. Or Activision up at 50x for similarly uninspiring growth. Could always buy Amazon on the moon at 150-200 times earnings, and wait a decade until their earnings catch up. There's always the exciting Microsoft, almost zero inflation adjusted growth for a decade ($17.6b in net income for 2008), in exchange I get to pay 30x earnings.

I guess there's always Walmart. I can pay 23-26 times earnings, for a company that has had falling earnings for years. Or 28-30 times for 3M, where I can get years of zero growth for that nice fat multiple.

And so on and so forth it goes, across the entire spectrum.

Investors were begging to get crushed up at Dow 26k. The recent surge into the market by retail investors is one of the more classic indicators that a bull run is done. They universally arrive late to the party.

<comment><USER74> But where do you put your money in a time like this?

</comment></comment></comment><comment><USER75> They are likely related, but it sure would have been interesting if the market went down 2000+ points at the same time Bitcoin was surging upwards.

<comment><USER30> But that didn't happen. BTC failed today's test that it's a "store of value / gold alternative"

</comment></comment><comment><USER76> Must be investors pulling all their money out of stocks to put in crypto!

<comment><USER34> Please tell me you're being sarcastic.

</comment></comment><comment><USER77> anyone watching daily technicals would have seen the RSI and MACD dropping last week, this should not be a surprise to anyone but noobs

<comment><USER78> And how many times have RSI and MACD droped and market not collapsed?

You get zero credit for predicting a drop after it happened. And also little credit for "predicting" something based on any indicator with frequent false positives.

Saying "I knew it" because one of 50 indicators showed something the day before is no different than what's happening in non-reproducability of research. State claims and indicators before and shows a track record of prior claims. But please don't after the fact claim "you knew it", everyone is a "newb". It subtracts from the conversation.

<comment><USER4> To be fair, he said "not a surprise" rather than "predictable with 100% certainty". However you can't trade on not being surprised, you have to take a position.</comment></comment></comment>


Differential Forms and Integration (2008) [pdf] - <AUTHOR> https://www.math.ucla.edu/~tao/preprints/forms.pdf <comment><USER2> On a related note, and seeing that some people around here are interested to learn the topic from different angle: Gerald Jay Sussman (among others, co- author of _Structure and Interpretation of Computer Programs_ ) has co-written a book on differential geometry called _Functional Differential Geometry_.

It builds up the theory of differential geometry using Scheme, just like SICP and SICM, and is a fantastic read for programmers wanting to grasp the topic in a more familiar language.

It is available for download for free on the publisher's website: [https://mitpress.mit.edu/books/functional-differential- geome...](https://mitpress.mit.edu/books/functional-differential-geometry)

<comment><USER3> That is damn interesting, and probably worthy of its own submission.

FYI for everyone looking for the download link, it's a bit hidden, so here it is: [https://www.dropbox.com/s/t3si4b99ijqyhyk/9580.pdf?dl=1](https://www.dropbox.com/s/t3si4b99ijqyhyk/9580.pdf?dl=1)

Licensed under Creative Commons BY-SA, too.

</comment></comment><comment><USER4> I took a Differential Geometry course in university. The course covered basic theory on smooth manifolds and Riemannian Geometry. While I did appreciate the beauty of the subject from a theoretical perspective, I have to admit that I somewhat lacked intuition for the material, especially with regards to differential forms. I understood that their properties make sense to define the notion of integration on a smooth manifold, but never really saw whether they had any purpose besides using them for integration. Even in their use in integration they were kind of a mystery to me, if I recall correctly we just defined integration on subset of R^n, where differential forms played the same role as d_{x_1}d_{x_2}...d_{x_n}, which is known from the riemann integral, but then to define integration on manifolds, we just used the pullback of the charts, which didn't alleviate any of the mystery and didn't add anything about why differential forms themselves are supposed to be important. I wish I had taken some physics courses, where vector calculus is used heavily and that might have helped some, but in the end I was somewhat disappointed, because even though taking the course certainly did make me a better mathematician, I still didn't have the feeling of really completely grasping the concepts, even though I could prove statements.

<comment><USER5> If you feel that pullbacks by charts conceal the intuition, you can work with manifolds that are embedded in R^n. Differential forms are still the "right way" to do integration on these manifolds but now can be defined in terms of the coordinate system of R^n. Then you can do cute tricks like seeing that if you want to know the area of a region on the plane, you can compute it by integrating dx ^ dy over the area. OR you can compute it as x dy over the boundary since d(x dy) = dx ^ dy. (Where ^ is the wedge operator.) This means you can And x dy can be integrated mechanically by a planimeter [1]. And this is also how you would compute the area of a region in software given its boundary!

There's some other uses. They form the basis of De Rham Cohomology [2] which is a useful and computational way of describing topological properties of a manifold (recall how Stokes's theorem and friends show how the topology of a space constrains the integrals of differential forms).

Another thing is that they're specific kinds of tensors on the manifold. Tensors represent basically all the information we might be interested in about a manifold (for example, its curvature). Differential 1-forms are "dual" to vectors and are therefore important to building more complex tensors (higher tensors take in some number of vectors and 1-forms and output a value).

And just as regular integration and differentiation relates to solving of differential equations, differential forms are needed for differential equations that are on a manifold.

[1] [https://en.wikipedia.org/wiki/Planimeter](https://en.wikipedia.org/wiki/Planimeter) [2] [https://en.wikipedia.org/wiki/De_Rham_cohomology](https://en.wikipedia.org/wiki/De_Rham_cohomology)

<comment><USER4> < Another thing is that they're specific kinds of tensors on the manifold. Tensors represent basically all the information we might be interested in about a manifold (for example, its curvature). Differential 1-forms are "dual" to vectors and are therefore important to building more complex tensors (higher tensors take in some number of vectors and 1-forms and output a value).

This was how differential forms were introduced in the course. I understood all of this from an algebraic standpoint, but I was lacking any geometric intuition for differential forms whatsoever. Say you have a k-form on some manifold and you evaluate it at some point which gives you an alternating covariant k-tensor. Then when you evaluate that at k tangent vectors at the point you get a scalar, does this scalar have any geometric meaning? Does it measure anything? Later when we did Riemannian manifolds and introduced the volume form that was at least a little more intuitive, as far as I remember, but general differential forms were intuitively a complete mystery to me. Also I kind of got their usefulness in an algebraic sense when we did some typical vector calculus calculations using the concepts of divergence and curl, but I didn't have much intuition for these concepts since I don't have a physics background and only worked with vector fields in this abstract setting. Unfortunately we did not cover De Rham cohomology. Thanks for your answer, I will take a look at planimeters.

<comment><USER6> The first 10 pages of the following link may be helpful; it shows probably the simplest concrete nontrivial 2-form:

[https://math.berkeley.edu/~wodzicki/H185.S11/podrecznik/2for...](https://math.berkeley.edu/~wodzicki/H185.S11/podrecznik/2forms.pdf)

The first example there is: given a base point X and two vectors V,W based at X, the 2-form gives the "signed" area of the parallelogram spanned by V and W. Determinants (which measure n-dimensional parallelograms), when viewed as functions of their column vectors, have all the properties of differential forms.

Differential forms are a bit like generalized determinants and in a sense specify a way to measure something like an abstract volume in the neighborhood of a point of a manifold, in such a way that the Jacobian needed for changing coordinates is "built in".

</comment></comment></comment></comment><comment><USER7> For anyone wanting to learn more about this, I highly recommend _Advanced Calculus: A Differential Forms Approach_ by Harold Edwards and _An Introduction to Manifolds_ by Loring Tu. The former reads almost like a novel and is a real treat of mathematical exposition. It's also a little quirky which is always nice. Tu's book is simply the gold standard of an introduction to the mathematics of manifolds and differential forms. It is the most concise and straightforward introduction to the full theory. It is also a wonderful book.

<comment><USER8> I love Hubbard & Hubbard, which is also great as it's an introductory text. It's been used often at Harvard Math 55 and some much simpler courses:

[http://matrixeditions.com/#vec](http://matrixeditions.com/#vec)

<comment><USER7> That is indeed a very good book. Although I would say that some of the notation in it is non-standard, for better or for worse. Tu is the most consistent author I have ever seen with notation, and that matters a lot in smooth manifold theory and differential geometry.

Another good book is _Advanced Calculus: A Geometric View_ by James Callahan.

<comment><USER9> > Another good book is Advanced Calculus: A Geometric View by James Callahan.

Thank you for this! For those of us who had real difficulty with Advanced Calculus, Callahan's methodical, visual, generous approach is deeply felt and appreciated. I did not know of this book until now and immediately found myself absorbed. It's embarrassing to admit, but as one who loves mathematics yet seems to struggle and stagnate more often than everyone around me, I often want to ask for, and indeed need, a bit of hand-holding. Callahan is a wonderful guide in that sense. Thanks again.

<comment><USER7> No problem. It is a great book.

Definitely check out Edwards' book I mentioned above as well. It is a gem of a book. Although it doesn't use matrices and instead uses linear expansions, it is still brilliant. The first three chapters give an exposition of the theory, and then the next three go back and prove things. So if anything, take a look at the first three chapters and then the later ones on applications and extensions. It also has a geometrical viewpoint.

</comment></comment></comment></comment></comment><comment><USER10> Can anyone recommend a good introduction to differential geometry and forms? Does something analogous to "Visual Complex Analysis" exist for the topic? I have been curious to learn for a long time but, for whatever reason, always lose my way at some point with articles like this. I come away with some feeling that I understand what's going on and yet I can't say I have any concrete intuition for what a form or a manifold is despite knowing the formal definitions. I feel like applied examples would help, but at this level of math that seems to entail going on a side quest to learn a lot of difficult physics first. (Or alternatively, doing a lot of proofs, but that feels futile without having a tutor/mentor to check them.)

<comment><USER11> A Visual Introduction to Differential Forms and Calculus on Manifolds by Jon Fortney.

[https://www.amazon.com/Visual-Introduction-Differential- Calc...](https://www.amazon.com/Visual-Introduction-Differential-Calculus- Manifolds- ebook/dp/B07QLN9B1C/ref=sr_1_3?dchild=1&keywords=visual+geometry&qid=1590139975&sr=8-3)

<comment><USER12> I got this recently from Springer directly, and just as a psudeo-warning, this is a "print on demand" book, at least the one I got was (it said so when I ordered it, so I was properly warned). Now, the print is actually pretty high quality and so is the binding, and it's a large and beautiful book. My only complaint is the paper of the pages is a bit thin, like regular printer paper stock, as opposed to the thicker glossy paper I was hoping for and that would be usual for a book this size. When you're leafing through it and a page is lifted, you can often see the content on the opposite side showing through. That can be distracting and may bother some people.

BTW: If you buy from Springer, you get a free pdf of the book immediately while you wait for your physical copy, because of the delay for print on demand. They say you don't actually "own" the digital edition (can't remember the exact wording), but I can vouch that it's not time-limited. It's a very good deal.

<comment><USER10> Having gone through two chapters now, I also feel the need to caution others that the amount of typos in this book is simply jaw-dropping. The conceptual explanations in the text are generally excellent, but it is simply impossible to get through a page without hitting a substantial number of mistakes. I'm left wondering if there are errors I'm not catching on my own that are going to affect my understanding. I really hope a cleaned up second edition is on the horizon (hopefully with answers to some of the in-line exercises).

</comment></comment></comment></comment><comment><USER13> I don't think the distinction between the signed and unsigned integral exists for the most general integral, the Henstock-Kurzweil integral. (I could be wrong, but an orientation seems to always be implied in being able to compute a Riemann sum over a tagged partition.)

This distinction is probably related to the Lebesgue integral's inability to integrate functions unless they are absolutely integrable (since it needs to be able to compute the positive and negative components and take the difference, which being finite to make sense, must be absolutely finite) and is distinct from the Henstock-Kurzweil integral which works directly with a tagged partition of the underlying set (which implies an orientation) and is able to integrate (some) functions which are not absolutely integrable.

Nevertheless, moving to differential manifolds introduces problems for the Henstock-Kurzweil integral becames the local orientation in charts does not always induce a sensible global orientation. However, integration on a manifold isn't so much integration of a function of several variables as it is integration of several functions of several variables. That one needs additional machinery to deal with the "several functions" part is unsurprising.

I can't recommend studying the Henstock-Kurzweil integral enough! Strangely enough, despite being more general, it is far more approachable than the Lebesgue integral.

<comment><USER14> I'm not sure gauge integrals are really "the most general integral". As you say, it doesn't work as well as the Lebesgue integral in multidimensional settings, does it? It also needs a bit of a tweak to give you the analogue of Stieltjes integration so you can unify sums and integrals, I believe.

<comment><USER13> They are the most general in the sense that there are Henstock-Kurzweil integrable functions that are not Lebesgue integrable and that other integrals that are also more general than the Lebesgue integrals are equivalent to the Henstock-Kurzweil integral.

It still works better than the Lebesgue integral in the multidimensional settings, since it is trivial to create a product f(x)g(y) of two functions which will not be Lebesgue integrable but is Henstock-Kurzweil integrable.

As for generalizations to generalized functions, my preference lies with Colombeau algebras over Schwartz distributions, in any case. Where at least there is an arithmetic of the generalized functions.

</comment></comment></comment><comment><USER15> It makes me feel good to know that Terence Tao spends any time thinking about integration - I would have thought that would be like a normal person spending any time thinking about adding and subtracting.

<comment><USER16> Funny you should say that. In elementary school I tested well for abstraction but exactly in the 50th percentile for arithmetic skills. Just like rejecting how people taught me to tie my shoelaces, and figuring out something for myself, I fixed my arithmetic deficiencies. I went on to a PhD in math and I'm now a professor. People still think I tie my shoes funny, and I add funny. I think for myself.

It's a crippling misconception that talent is natural. Michael Jordan made himself the athlete he became; many people had his body but never got as far. Good mathematicians take conscious control of how they learn and think. Our tendency to go "meta" isn't restricted to math; it's applied to ourselves.

</comment></comment><comment><USER17> The Stein and Shakarchi Real Analysis text is a great read for learning measure theory

</comment><comment><USER18> this is his article in the princeton companion to mathematics

[https://www.amazon.com/Princeton-Companion-Mathematics- Timot...](https://www.amazon.com/Princeton-Companion-Mathematics-Timothy- Gowers/dp/0691118809)

a great (even if expensive) math book

<comment><USER19> Thank you! I was getting really strong "you've read this before" vibes from the article but couldn't place the source.</comment></comment>