Why has the quality of brick buildings declined in the last 100 years? - <AUTHOR> http://www.greenbuildingadvisor.com/articles/dept/musings/quality-issues-brick-buildings <comment> old-gregg The quality of modern construction (not necessarily brick) is a big pet peeve of mine and something I keep looking for answers.

The way I see it, some time right after WWII, people in US suddenly decided to live in a poorly built and ugly looking dwellings regardless of their income level. It is especially easy to see when looking at NYC buildings, some rentals are even explicitly advertized as "pre-war".

Examples of annoying trends in modern construction:

      - Low "hobbit" ceilings.
      - Short door frames.
      - Tiny windows.
      - Nearly non-existent noise/vibration insulation

Even looking at materials used for construction today, I can't figure out why everyone thinks that drywall-on-sticks is acceptable? Literally every multi- story home I've been in felt hollow and shaky if you jump on the 2nd floor because there's no mass anywhere.

This is clearly not a cost issue, I have taken tours looking at brand-new multi-MM homes in Austin, TX just for fun. While they all had top-notch appliances, finishes and a gazilion of square feet and bedrooms, they were also built using the same "toy" materials and used generally similar architectural patters as middle class homes.

What caused this change? It's like our collective mind suddenly stopped caring about tall doors, 10ft ceilings and solid feel of floors we walk on.

<comment><USER2> A combination of three things, IMHO:

1\. Labor specialization, meaning less of the home-buying market is savvy enough in the "handyman" sense to tell the difference. 2\. A move away from building the thing you're going to own, and building things that other people will buy later. 3\. Minimum standards for housing construction.

The third needs to be explained more - instead of aiming towards "building a good home", the construction industry aims to build the cheapest thing that they are legally allowed to sell (ie, meets building codes). While building codes do mean that there's a quality floor, competitive pressure means that nobody can consistently exceed the floor without getting out-competed by people who aim to barely meet it.

<comment><USER3> >"...less of the home-buying market is savvy enough in the "handyman" sense to tell the difference"

True. I don't know how the market works in the US but in the UK what typically happens is a developer owns the land but borrows short term money to build on it.

The incentive, therefore, is to complete the project as quickly and cheaply as possible. Residential houses are designed for ease of building not for quality.

A typical buyer will have a 90-95% mortgage and the completed house is signed off by a surveyor who is engaged by the mortgage provider. The only real concern is if the house will still be standing in 25 years time and nothing else. In effect it's a rubber stamping process.

The buyer is often too emotionally involved in the concept of owning a home to care less.

No sane person would complete the purchase of a new car if defects in build quality were so glaringly obvious but the same people do it with houses every day?

<comment><USER2> Yeah, that's roughly how it works in the US. Pre-WW1, though, there was much more of "buy land and materials, build a house yourself" going on. Like, sometimes you'd basically clear the trees from a plot and use the lumber from that to build the house.

That's what I meant by labor specialization - on the home-buying side, much fewer people can build a home or participate meaningfully in construction and remodeling.

</comment></comment></comment></comment><comment><USER4> Is the brick actually holding up the building? In many modern buildings, it's just a veneer, about 1cm thick. The steelwork holds it up. The new Box.net HQ in Redwood City looks like a brick building, but it's not; it's steel and concrete with about 1cm of brick on the outside.

There's some nice work being done with brick today.[1] Some of this is gentrification, built to fit in with existing brick buildings, or to imitate them in new construction. All those examples have recessed windows, although not structural stone lintels. Many lintels today are precast stone and decorative; steel is carrying the load.

Robotic bricklaying is here.[2]

In earthquake country, you really don't want tall brick buildings where the brick is structural. San Francisco is very anti-cornice; in even minor earthquakes, overhanging masonry cornices tend to fall off and kill people.

[1] [http://www.bdcnetwork.com/7-emerging-design-trends-brick- bui...](http://www.bdcnetwork.com/7-emerging-design-trends-brick-buildings) [2] [https://www.youtube.com/watch?v=Ppk4O7iyzPI](https://www.youtube.com/watch?v=Ppk4O7iyzPI)

<comment><USER5> > _Is the brick actually holding up the building?_

This was my thought as well. The modern building is likely just using the brick as veneer, even if it is full-thickness brick. It's likely concrete walls with brick layered over it. The fact that the brickwork is poorly done likely doesn't matter except aesthetically. If all the brick fell off the building would still be standing.

The newer building is indeed ugly, and the brickwork looks cheap and poorly done. But that doesn't mean the technology has declined. It means the technology has advanced to the point that the brick is just ornamental.

<comment><USER6> I fully expect that the brick is structural in those examples. My university had brick dorms "the bricks". They had brick exterior walls and cinder block interior walls. The brick walls were brick on the outside and the inside and only one brick thick.

<comment><USER5> If the interior walls are cinder block, I would expect the brick to be purely aesthetic. Cinder blocks don't need brick next to them for strength if built correctly.

</comment></comment></comment></comment><comment><USER7> Reminds me on a recent conversation at a maker space:

        How do you control it, a transistor and a oscillator?

        Nah, just an Arduino.

So with micro controllers we loose a lot of applied knowledge of analog circuits and I suspect something similar is going on in architecture. The hours a architect spends on learning about modern materials is not spend thinking about brick works, and consequently a modern architect is a lot worse at building brick buildings than a architect one hundred years ago.

</comment><comment><USER8> _> "Part of the blame, I feel, rests at the feet of the Modernist movement — a movement that idealized the cube and disdained roof overhangs. Modernist architects were ignorant of the entire concept of moisture management. The fact that thousands of Modernist buildings suffered water entry problems did little to deter architects from falling in love with Modernism and Brutalism. This tragic love affair contributed to the withering of age-old skills."_

I believe this is a fair assignment of blame. It's analogous to the complaints people have about some modern web design - total focus on appearance at the expense of usability or technical quality.

The architects produce buildings that look good on paper, because that's what wins the contract. The next client isn't going to go to their previous building and do a customer satisfaction survey on the users. Nobody ever does.

Edit: Incan stone construction is one of the great examples of ancient 'over'building: precisely fitted hand-carved stone, good for five centuries. And Rome has plenty of 2000 year old brick buildings, especially the Pantheon dome.

<comment><USER9> This was a good article but I think the authors assignment of blame is misplaced.

In my opinion the reason contemporary brick construction is not up to par with 100 year old brick construction is the same reason contemporary washing machines are not up to the standard of washing machines 100 years ago: The emphasis in making things now is on speed and cheapness, the emphasis 100 years ago was on quality.

The college dorm building was certainly thrown up in a fraction of the time, for a fraction of the price with a fraction of the labourers, than the bank building.

<comment><USER10> I will gladly trade a 100 year old washing machine (rusty and hand-powered, I assume) for a Miele.

I'm sure you have an argument here, but I don't see how washing machines further it.

<comment><USER9> You assume too much. Also this article is addressing the construction quality and longevity of brick facades. I was referencing the construction quality and longevity of washing machines, pre-war vs modern.

[https://youtu.be/baFaEvBywGc?t=22m40s](https://youtu.be/baFaEvBywGc?t=22m40s)

<comment><USER11> Back then, you could only buy expensive high quality ones. Only a few people could afford it. Nowadays, you can buy cheap crappy ones, as well as expensive high quality ones. What's the argument here? If someone will let me spend the equivalent amount of what these old houses cost back then on a new brick building, I will have them build just as good as the old ones. Actually, I'll have them build better, because the woodworking of the windows will be much better, the moisture barriers will be better, the insulation will be better, the quality of the mortar will be better, the concrete slab will be better (actually, 'it will have a concrete slab'), the roof tiles will be of better quality, the heating system will not suck, I can go on and on...

</comment></comment></comment></comment></comment><comment><USER12> The author admits to the limited comparison. I have a few other reasons:

1\. We actually care if our buildings are insulated now and withstand earthquakes.

2\. People are so wealthy here they don't have to get it right, they can always pay to do it over again. They don't care to put in the research to make sure it is done right. [0]

3\. Corollary to #2, we don't need our buildings to last 100 years because we expect the area to be overtaken by increased density by then?

[0] CSB: Person tells about friend that bought house in Las Vegas just prior to 2008, has enormous cooling bill because house doesn't have overhang to protect southern exposure from the sun and HOA won't allow her to alter it. Asks why the government doesn't protect her. I ask why she didn't do a little more due diligence before spending $300k. He hadn't thought of it that way and considers it.

<comment><USER13> How would any of the issues with the Dartmouth brick building in the article have been caused by #1?

<comment><USER14> I'm pretty sure they don't care about insulation that much at Dartmouth. There's a huge steam plant on campus, and all the brick dorms are equipped with old-fashioned steam radiators that have two settings - over-bearingly hot, and "boil my pot of ramen noodles." It's common to see the dorm windows wide open when it is -20 F in February, with students trying to regulate the temperature to a livable level.

</comment></comment></comment><comment><USER15> A bit more technical: [http://buildingscience.com/documents/insights/bsi080-tailor-...](http://buildingscience.com/documents/insights/bsi080-tailor- made)

Essentially, Holladay is complaining about the lack of water detailing, which is super important to the durability of brick. It doesn't need to be as fancy as his first example, as the link above shows, but you need someone to care about it.

Essentially, the issue building science specialists have with modernist architecture is that it often favors geometric simplicity over proper protection of the materials. Brick can withstand water, to an extent, but without drip edges and other details, it's quickly going to get damaged and ugly.

Note that building science nerds also tend to hate bumpouts and complicated rooflines because the air tightness and insulation details are hard to get right (and usually they just aren't done properly).

</comment><comment><USER16> The small house I live in is 100 years old, and built of brick. It is a tremendously (over-)engineered building: two layers of brick _even for interior walls_ , exterior walls are around 1 ft thick, and four massive chimney-breasts (although two were sadly removed by previous owners).

My theory is that they just had enormous amounts of cheap labour 100 years ago, and you'd never be able to build such a building today because it would be far too expensive.

<comment><USER17> In my experience the timber in buildings that old is of the sort that would be hard to find at any price these days, and ruinously expensive if you could. Single thick, long, flawless pieces used in places where several thinner, knot-filled pieces would be used today.

Exceptional (by modern standards) material, used in quantities that would be considered excessive even in _nice_ construction these days.

<comment><USER16> This is of course why reclaimed building materials are a thing (in the UK anyway). I could go to a place not 10 miles from here and buy a cast iron fireplace that was previously in a home very similar to mine. The irony being that a previous owner of my home probably chucked my fireplace in a skip in about 1980.

</comment></comment></comment><comment><USER18> Alright, too many mentions of survival bias and too much skepticism. There're large parts of some cities that are almost exclusively constructed from brick. It might be bias or it might not be.

It's clear that nowadays buildings are made cheaply. For example the construction of the regular American suburban "stick" house is just the cheapest and the quickest way put up walls and a roof. What you get is something that's badly insulated (both from weather and sound) and just isn't very strong, and the technique is getting traction in other parts of the world too, replacing concrete, beams and brick.

<comment><USER19> Yeah I don't think it's bias.

That would imply that there's no issues with the newer design when the article clearly showed where the wrong choices have affected the durability of the building.

</comment></comment><comment><USER20> It's an interesting idea worth exploring...

...but comparing a bank (a building that in 1891 had to LOOK expensive) and student flats (a building that has to BE cheap) results in the rather underwhelming discovery that because they had wildly different budgets with completely different aesthetic aims, they ended up with different built qualities. Shocking, isn't it?

If they want to make an apples-for-apples comparison, the author should come to the UK and compare our 1890 semi-detached with any post-70s new-build. There are certainly ecological issues with the older building (that are expensive to retrofit past) but the quality of building and workmanship is drastically better in the older houses.

And [at least in the UK] this isn't a case of crappy houses made of sticks falling down. With the rarest of exceptions, there is no "survivorship bias".

<comment><USER21> Student housing at a very expensive private institution. Not some council houses. So pretty fair comparison I think.

And that aesthetics should override competent construction technique is a bad idea, is also a fair criticism.

<comment><USER20> It's sweet that you think students get what their parents pay for. No. The briefest of glances lets you know exactly what Dartmouth instructed their architect to aim for: capacity.

The real reason it looks so poor is —as I did say before— their respective aesthetic aims. Dartmouth wanted something that looked New Englandy that holds dozens of students, while the bank wanted something that makes them look like they have all the money.

</comment></comment></comment><comment><USER22> If you are curious about this topic you should bring it up with some architects from different countries. From my understanding there are indeed regressions in building quality in some countries but it's not entirely clear what causes it other than decisions that have been made at the time.

In particular the brick did not decrease in quality but the way they were built did. For instance for a while people paid less attention to protecting buildings from water damage to achieve more interesting designs.

A particular crazy architectural style that suffers a lot from this is British brutalist architecture.

<comment><USER23> Brutalism gets everywhere in modern british arcitecture. The idea that any archtiect should be designing a flat foor bulding in, say, Scotland is totally bonkers.

<comment><USER8> [https://en.wikipedia.org/wiki/St_Peter's_Seminary,_Cardross](https://en.wikipedia.org/wiki/St_Peter's_Seminary,_Cardross)

It's a beautiful ruin, but it seems never to have been a properly functioning building. Artistic success, total waste of resources for church that built it.

<comment><USER24> Oh yes that's quite the nasty bit of concrete.

<comment><USER23> I would love to know the mindset and thought process of Brutalist architects and admirers who see that and see beauty whilst the majority of the rest of the world sees a broken down leaking eye sore.

We are so far apart it is like trying to understand and alien.

I have seen a scant handful of Brutalist building that I consider fine works of craft but the gob smacking majority are pitiful piles of concrete and exposed trusses.

<comment><USER25> I don't think I've ever seen a Brutalist building that I consider good. Worse still, stupid architects get them heritage listed so we can't even replace them with actually useful buildings (i.e. [https://en.wikipedia.org/wiki/Cameron_Offices,_Belconnen](https://en.wikipedia.org/wiki/Cameron_Offices,_Belconnen))

</comment></comment></comment></comment></comment></comment><comment><USER26> Survivorship bias and structural integrity aside, I suspect it's all about the cashflow.

The bank was built in 1891. The FDIC wasn't around until 1933. The appearance of wealth and institutional stability was a very important marketing tool to late 19th-century bankers wanting patrons to trust them with their money.

The dorm houses kids fresh out of high school who can't / don't want to live off campus. I'd guess the building is attractive enough to most people to avoid negative attention, and -- as the article indicates -- it obviously isn't swaying money away from Dartmouth, so why bother?

</comment><comment><USER27> More broadly on this subject, I recommend that every software engineer read the book _How Buildings Learn_ , by Stewart Brand. It's a book about the lifecycle of buildings, design compromises, and how buildings are altered and repurposed over their life. It's a fascinating way to think about software as well.

</comment><comment><USER28> Could it be survivor bias? What if the cheap shitty hundred-year-old buildings are torn down or covered in plaster or siding, thus leaving only the good specimens?

</comment><comment><USER29> This is a clear example of survivorship bias.

Buildings from 100 years ago that still stand today necessarily must have been those that were most carefully constructed or those that have been thoughtfully preserved. This creates a biased comparison between the highest quality buildings of the past and an average (or perhaps worse than average) building from modern times.

This article could conclude that not all brick buildings today are superior in construction to the highest quality buildings built 100 years ago, but making a more general statement would be a fallacious extrapolation.

<comment><USER30> And to bring that idea home: contemporary flimsy construction is also a function of local building codes. In 2004 I was in a Florida house built in 1988 which structurally resembled a concrete bunker outfitted with heavy duty crank windows. This was required construction at the time. A hurricane showed up mid August with 140 mph (225 kph) winds and two things in particular were impressive: how well the structure survived the hurricane essentially unscathed (other than damage to it's pool cage screening) and witnessing how well palm trees folded their foliage to weather the onslaught. Apparently after 1988 they had lightened up on the building codes and cheap 2X4 frame construction was allowed for two story dense pack condos in the surrounding area. These did not fare so well. In one case a large pine tree was snapped at the base and hurled through the side of a frame condo complex like a battering ram, demolishing the whole structure. The complex had been evacuated before the hurricane struck so apparently there were no casualties. The moral of this story is that if you mandate good construction then that's what you get. Leave loopholes for cheap construction and that's what you'll get (and it won't suffer the rigors of time very well).

</comment></comment><comment><USER31> Where are brick buildings being torn down left and right? I challenge the survivorship bias argument as where I live in the US east coast multiple cities push for historical status on buildings past a certain age in order to retain character.

<comment><USER32> My 1950 brick building is 1/3 constructed from re-used brick. Many houses built in the 1960s in my area are also built of reused brick. There must have been some degree of brick teardown going on.

Even now we have trouble with people stealing brick buildings. Unused houses are sometimes set ablaze by brick thieves, then later they come in the night and cart off the bricks.

<comment><USER8> _stealing brick buildings_

This sounds totally bananas, where is this? Are the bricks made of gold or something?

<comment><USER33> This is a problem in parts of St. Louis, MO. The brick is of high enough quality that people will steal them for resale from abandoned buildings. Naturally, this leads to the building collapsing which causes even more issues for surrounding area.

</comment></comment></comment></comment><comment><USER34> There are some other great explanations in this thread (survivor bias seems very plausible), but I'll throw out another based on my experience with other construction trades: economics.

If you look at old buildings, you tend to notice that they also have a lot of intricate plaster-work that you never see anymore. Why? Because it used to be much cheaper to hire skilled labor than it is today. You can see a similar trend every year in the Christmas Price Index, which tracks the cost of the items in the 12 Days of Christmas song. The prices of goods tend to stay stable, while the price of labor tends to increase significantly.

For our brick buildings, I tried to find the best numbers I could, and here's what I came up with: In 1894, bricks cost about $5.70/thousand [1], which is $165.51 in today's dollars Today, you can get bricks wholesale for $220/thousand - and that's what I found online, I imagine an actual wholesaler is less. [2] That's an increase of about 37%

For the bricklayer, the average wage in 1891 was $4/day, which is about $110 in today's dollars [3]

Today, the median bricklayer pay is $24/hour [4], which is $192 per 8 hour day.

That's an increase of 75% in the real wages of the bricklayer, and it means that the rate labor costs have increased is double the rate of material costs.

In 1891, it may have made financial sense to pay for a bricklayer to make intricate, high quality buildings. In the past few decades, it's likely that's no longer the case.

[1] [https://books.google.com/books?id=Oo4oAAAAYAAJ&pg=PA953&lpg=...](https://books.google.com/books?id=Oo4oAAAAYAAJ&pg=PA953&lpg=PA953&dq=average+price+brick+1891&source=bl&ots=GcEOPaUc51&sig=NleYQCrOeeo04wtGQazDrf-4WFc&hl=en&sa=X&ved=0CB0Q6AEwAGoVChMIyoCb_tn8yAIViiomCh07oAPV#v=onepage&q=average%20price%20brick%201891&f=false)

[2][http://brickbroker.com/brick.html](http://brickbroker.com/brick.html) [3] [https://books.google.com/books?id=cNdEAQAAMAAJ&pg=PA722&lpg=...](https://books.google.com/books?id=cNdEAQAAMAAJ&pg=PA722&lpg=PA722&dq=wage+bricklayer+1891&source=bl&ots=yl05RZTmSC&sig=ezss_Em2mx16u76THQi7eTaR8xY&hl=en&sa=X&ved=0CCsQ6AEwA2oVChMIqIWbodr8yAIVTOImCh3fKQED#v=onepage&q=bricklayer's%20wages&f=false) [4] [http://www.payscale.com/research/US/Job=Bricklayer/Hourly_Ra...](http://www.payscale.com/research/US/Job=Bricklayer/Hourly_Rate)

<comment><USER35> I think you're on the right track but your comparison fails to take into account the productivity of the bricklayer. A good bricklayer today ought to be more productive than an 1891 bricklayer, because he has motorized mixers, vehicles to move bricks to the right place, laser lines to level his rows, etc. Even in a craft that seems legendarily nontechnical, you have to give some credit to technological advancement. But it's still probably not enough to fully compensate for the 75% increase in labor cost.

<comment><USER36> You couldn't possibly hire the bricklayer directly today. The bricklayer would be hired as a subcontractor by the general contractor who would apply a surcharge.

<comment><USER37> Yea, and I see this as one of the main reasons, the quality of work is declining instead of improving (due to technical advances). In my country, when you build a building today, you hire a builder company. This company does _no_ building themselves. They buy the parts of the building from subcontractors and some times the subcontractors buy the service needed from sub-subcontractors. And the company that finally does the job, some times, they even do it not with their own workers, but hire some cheap temporary staff to do the work.

So finally, who is to blame, when the window is not even? The builder? No! He did nothing. The windowing subcontractor?? Technical yes, but practical he just used hired workers. Some times ago, it was possible to say: Here we have a good company, with good reputation, the workers are proud to work for it ... Today, it is just a blaming game -- and when one of the subcontractors is sued because of bad work, they file bankruptcy, because there is also no financial basis -- the companies are just empty shells.

What also adds up to this is, that on every level of this game, only the price of the service is evaluated today -- not the quality. I also saw cases, where the builder company was a big one with great reputation, but the execution was awful! The reason: Bad contractors.

Another reason in my country is, that the requirements for workers in the building sector have been deliberately drastically lowered by the government, to make way for even cheaper work.

Today, (at least in my country) one that wants a house for his family to be build, has no means to decide, if the company will succeed and make a good house or will build a horror house. In most cases, there will be several topics where the execution was bad or really bad and you can call yourself lucky, when the additional costs after the house was finalized are moderate.

There are some really bad cases, where families thought the house would be ready in time and canceled their rent-flat just to be on the streets afterwards, because their house was not ready even months after the deadline. Some where never finished.

</comment></comment></comment></comment><comment><USER38> We have the same issue here in Australia. The quality of recent brick work is terrible, even the bricks are worse. It seems brickies are unable (or unwilling) to lay bricks anymore.

</comment><comment><USER39> Survivorship bias is a really important caveat: [https://en.wikipedia.org/wiki/Survivorship_bias](https://en.wikipedia.org/wiki/Survivorship_bias)

Many cheap brick buildings from 100 years ago are gone, where the high quality ones are more likely to remain.

Also, steel Lintel are often used over windows in brick buildings. They don't last as long, but are fine for cheap construction that is not expected to last. AKA the kinds of building that are unlikely to be around in 100 years.

<comment><USER40> My last house was built in ~1936. It was cheap for the time, but the entire estate of houses it sat in was complete - virtually nothing had been removed. The form of the buildings had changed somewhat (extension for bathroom instead of toilet in the garden), but the brick walls were incredible and the internal timberwork (joists, frames, etc.) was all hardwood of a quality that would be very expensive now.

My current house was built in ~1985. The brick quality isn't bad, the walls are much straighter, but the wood is cheaper and the materials thinner and lighter. It might be the case this place will last 100 years, but I wouldn't bet on it. It's a middle market house, for the time, not cheap but not high end.

While survivor bias is important, where I live (London) the main reason houses from 100 years ago aren't around now is simply the war. The stuff from then that's still about - including "cheap" factories and other stuff - is now wildly fashionable and still well-built. Stuff built in the 50s was laughably awful and a lot is gone, stuff from 60s and 70s is going the same way. There are definitely other things going on.

<comment><USER38> I think one thing is buildings are now are built closer to their required engineering tolerances. In the past many building were massively over engineered, while modern buildings seem to be built for their exact expected lifespan.

The one thing I really hate about most modern buildings here in Australia is the ceiling height has been reduced. A lot of modern buildings have ceiling heights around 7' while old buildings will have ceilings of 10' to 12'.

<comment><USER41> Shorter ceilings are better for climate control, though. No need to heat up a bunch of air that just floats around over your head.

<comment><USER42> Not a huge concern in most parts of Australia... Having high ceilings (and fans) is actually an advantage.

</comment></comment></comment></comment></comment><comment><USER43> As I sit here in a rather old house (1920's) though never very expensive house I would say there are good and bad things about it. There's very little insulation, the heavy exterior is only a couple inches from some sort of plaster board on the inside causing many electrical boxes to be shallow. They really didn't care about the price of heating the house when they built it or maybe they did it to be cheap, but in any case that cost has gone way up. I do like an actual wood floor and heavy beams used in the construction of the basement and such. The plumbing is sometimes far more creative then is easy to fix now and I've found myself just cutting sections out and replacing it. I actually have some pipes made from lead going out so they can be bent in curves. Terracotta drains in the yard probably need to be replaced. The wiring was the first thing I replaced, knob and tube without grounds was just scary. O, and since the entire house was painted (yes they painted the formed bricks, not exactly like in the article though still bricks) with lead paint I certainly wouldn't eat something grown close to the house. Also I have steam heat which is interesting all by itself. So all in all, a not super expensive old building tends to be a lot of work these days and I would rather have a newer even if flimsy construction next time. I think I'll go along with the commenter who said the surviving old buildings are a bias because they are generally the best of the best of what was built in that time period.

</comment><comment><USER44> There are almost no 100 year old brick buildings in San Francisco. Why? Because there was a big goddamn earthquake in 1906, and unreinforced masonry (which is to say, functionally almost all of it) deals badly with earthquakes in general. It deals especially badly with them when they are built on landfill.

There are also lots of mentions of survivorship bias, which is extremely relevant here.

Now that said, I find modern construction to be badly done in general, because it is almost all of it erected as cheaply as possible—and as cheaply as possible as measured by the shortest possible term metric. There is good stuff done still, and it is arguably cheaper over the ten year run or longer, but that's not what people buy and so it's not what the developers make. I'd like to claim this is shortsightedness but I can't shake the feeling that it's because real wages have been stagnant or sometimes declining since around 1972. There just isn't the money to spend.

N.B.: there are a lot of reasons why modern lumber seems like so much crap. About 95% of it is because folks are unwilling to pay for good lumber, as described above. Quality lumber, even quality construction lumber exists, but it's significantly more expensive than #2 common. Of the remainder, it's worth remembering that modern 2x4s are tend to be farmed in sustainable fashion using fast growth species like Douglas fir or Southern yellow pine. The stuff we were building with in the 30s and 40s? Quite a lot of that came from old growth forests, now irrevocably gone.

</comment><comment><USER45> I live in Hanover, NH -- the town mentioned in the post -- and see that building every day. I also know the architect that designed that building personally, and would be happy to forward any questions to him.

<comment><AUTHOR> I don't have any specific questions, but I'd love to see his response to the article! I'm pretty sure that Martin would add it to the bottom of the original if desired.

</comment></comment><comment><USER46> There are some modern construction techniques that make me nervous:

One is pre-stressed concrete. This has replaced I-beams for highway bridges. The problem here is how do you inspect them? With steel I-beams you can use your eyes. With concrete maybe you need some kind of ultrasound equipment to check the tension cables? Do you trust those responsible for long-term maintenance to do it?

Another is engineered wood I-beams for houses. Basically these are floor joists made out of plywood. How long will they last? What happens if they get wet? If there is a fire the house is gone because the floor joists will be ruined by the water to put the fire out.

There were certainly mistakes in the past as well. One is building with cast- iron beams. They look nice, but they crack.

<comment><AUTHOR>
      If there is a fire the house is gone because the floor
      joists will be ruined by the water to put the fire out.

Do you have more information on this? I've known about the increased direct risk from fire, but haven't seen anything about damage from temporary water contact.

The only information I can find doesn't seem to agree with this, although it doesn't specifically prove otherwise: www.woodbywy.com/document/tb-213

<comment><USER46> Well I went looking for this and it's not as clear as I first thought. The fire risk is the biggest issue. The webbing for "TJI" is made out of OSB, and it seems there is definitely a long absorption time for this material so I'm thinking the collapse risk from water during firefighting is not all that high. Nobody is recommended ignoring long-term dampness (like from a leak) and the manufacture will certainly void the warranty.

</comment></comment></comment><comment><USER47> This sort of "commodification", for lack of a better word, is visible in many areas, I think. I was thinking about this lately in relation to tools. It's great that you can now get tools for unbelievably low prices compared to, say, 50 years ago. This _is_ a big win in many instances, because a shitty tool is often better than no tool at all, and it opens up access for many who would never be able to afford the old tools.

The flip side, however, is that it's devalued quality. It's remarkably difficult to actually find high-quality stuff these days. Even what used to be high-end brands have been bought up by some conglomerate that is now selling cheap Chinese versions under the old names.

There's still a market for quality, of course. You don't use tools from Harbor Freight when building rockets, but you'll never see those in any store you visit and they're likely to be priced far outside the reach of a normal person. It's like the middle ground has been lost, most stuff is cheap and low quality and then there is this small high end of really expensive stuff.

</comment><comment><USER48> Isn't this simply an instance of [https://en.wikipedia.org/wiki/Survivorship_bias](https://en.wikipedia.org/wiki/Survivorship_bias)?

The only brick buildings you can still look at from the 1800s are the ones that were built very well - all the shoddily-constructed buildings from that era have since disappeared.

<comment><USER49> Here's an example of a shoddy building from over a century ago that, through a historical quirk, is still around: [http://www.marketwatch.com/story/san- francisco-shack-startin...](http://www.marketwatch.com/story/san-francisco- shack-starting-at-350000-2015-09-29)

Yeah, the dorm in the linked article is totally better than that building. So while there are good buildings from that era, let's not kid ourselves, there were also a lot of horrible buildings that are rightfully no longer around. I would be willing to bet that the average quality of new construction is better now than it was then. If nothing else, the pervasive use of aluminum/vinyl siding and tar-asphalt shingle roofs yields buildings that better withstand the elements that old-style painted wood.

</comment></comment><comment><USER50> I saw this brickwork on a building in nyc's financial district on a building maybe around 50-100 years old.

[https://plus.google.com/111337360985340071974/posts/KkDyX34u...](https://plus.google.com/111337360985340071974/posts/KkDyX34uZop)

<comment><USER51> That's structural brick covered in stucco, which was pretty common in American cities in the 18th and 19th centuries. You see it a lot in areas with low- quality clay, since the resulting brick is porous and brittle, necessitating a stucco covering to protect it from the elements and not look awful. It might not be poor construction, just ugly because it's not intended to ever be seen. Of course, by design the stucco needs to be replaced every few decades, so who knows if it's been kept up.

That contrasts with the article's 1891 example of a building where the brickwork was both structural and decorative, requiring maximum attention to detail.

<comment><USER50> Did you zoom in on the brick underneath? It's helter skelter.

</comment></comment></comment><comment><USER52> He is right about a couple of things, though he does not seem to have much of a grasp about buildings in general.

He is right that sills (whatever material they are made of) should always protrude. I agree that the 1970's and 80's will probably be considered the low point in building (and were certainly the low point in automobile quality).

He apparently doesn't understand that the brick header in the older building is actually weight-bearing while the one in the newer building is a veneer covering a poured-concrete structural header.

He misses the main point: the older building is much better quality because it cost much more in relative terms. Buildings, like most of our modern products have declined in quality because we don't spend as much on them. But we have far more stuff - buildings and everything else.

</comment><comment><USER35> In Somerville, MA there is an area with some converted loft buildings including new construction loft-style buildings. The new building walls use masonry blocks (large grey blocks) for structure, with decorative brick on the outside. On the inside, there is a cavity for insulation and wiring, and an interior brick wall.

The masonry work is excellent, and is probably the best way to create a wall that looks like brick inside and out yet meets modern insulation demands. But it is a gratuitously expensive construction technique to try and make a building look old and classic. If you don't value that particular aesthetic, you would select other materials. If you want to pander to that aesthetic but don't have a premium loft budget, you might end up with crap like that dorm.

</comment><comment><USER53> How do these buildings compare in cost, adjusted for inflation?

A lot of examples of "superior" technology from 19th century turn out to be expensive stuff created for upper class, compared to mass-produced items of today that are affordable for the general population.

</comment><comment><USER54> Is there a non-paywalled version?

'This article is available for GBA PRIME members only'

<comment><USER55> Easily ripped-off because their paywall needs a new word to describe simultaneously terrible, useless and laughable that isn't Donald or Trump. In most desktop browsers, press <ESC> (or stop on mobile browsers) to stop loading content while the page is still loading in just the right time window and the paywall ask will be less likely to popup (but still nondeterministically succeed sometimes).

Or read just the the text here:

[https://gist.githubusercontent.com/anonymous/7eea331af1ff2fe...](https://gist.githubusercontent.com/anonymous/7eea331af1ff2fe088c2/raw/d87d8abce8d8f0788c43fab8ad3f5bc6f30c5f89/gistfile1.txt)

</comment></comment><comment><USER56> Bank buildings built before 1929 tend to be massive masonry structures with greek columns, marble, etc. Ones build later tend to be cracker boxes in strip malls.

My theory is that the older banks needed to impress their clients with stability, conservativeness, safety, responsibility, etc. After FDIC, customers looked to the government for that, and so banks no longer needed to spend the money on the building.

The massive, glittering vaults are sadly gone now, too. The money exists as data on a server somewhere, little need for a vault.

<comment><USER57> > After FDIC, customers looked to the government for that

Or an alternate theory: bank owners used to be local businesspeople, who would have been (rightly) embarrassed and ashamed to erect a shoddy and short-lived structure in their hometown. Now banks are at least regional, if not national or global, and care more about saving a few pennies for shareholders than they do about the communities they inhabit.

Combine this with the fact that consumers and "fellow citizens" don't give a crap about good buildings and good urbanism, and here we are with crackerbox drivethrough shite that nobody gives a damn about because it'll be bulldozed in 30 years, after a brief stint as a laser tag venue.

<comment><USER24> This is close to what I think. To a great extent buildings have been commodified. And businesses typically do not own buildings, they are tenants.

The bulldozed in 30 years attitude is post war nihilism in a nutshell. (In thirty years will be living on mars or dead from nuclear fire)

</comment></comment></comment><comment><USER58> I don't buy any of it for even a second.

On my way to work, they're building this wonderful brick sidewalk. While still just a side walk and not a building, it's remarkably well crafted and detailed. I think we CAN do it, we just choose not to, economically.

I think somebody would rather save a lot of money and build something "good enough" these days than invest in craftsmanship. Also, I bet you don't have to look far to find a bunch of counter examples in modern times.

<comment><USER59> Someone might be able to do it, but they're not easy to find or cheap.

There was a structural brick house that remained an eyesore in a DC neighborhood for years after a car accident demolished part of its cylindrical masonry wall (picture a round castle tower). The owner gave the reason that the masonry skills to construct this type of feature were not something easily found, and had been a sort of lost art, and they had been looking for a long time before finally getting it repaired.

</comment></comment><comment><USER60> I wonder if the decline of labor unions is a factor, or some similar thing that affects the willingness of people to make a career of a skilled trade.

</comment><comment><USER61> The dramatic increase in the cost of labour compared to the cost of bricks and mortar has been a major driver in the elimination of detail on houses and buildings. Now we engineer things to snap together. Wires and pipes etc all suffer from this problem as well. We can actually make better brick work, with longer lasting mortar - as long as we want to pay for these details

<comment><USER62> One interesting thing that I found out, having renovated a loft in a brick building from the early 1900s, is that modern mortar is much more friable and shorter-lived than older mortars (specifically, European recipes) made with a higher proportion of lime. The old mortars flex more effectively, while moderns compounds crack and spall. When we repointed our building, we found an English stonemason with a background in historical buildings (it's not cheap, architecture). He had worked on renovating Roman-era buildings in Bath, where they found that mortar laid down thousands of years ago had survived completely intact, requiring often very minor repairs. It's sobering to think that Roman building technologies will outlast those of our own age.

</comment></comment><comment><USER63> You can see the results of this all over NYC. A building down the street from where I live has had scaffolding around it for over 2 years as they replace the bricks (building owners have to test the bricks ever 5 years in NYC if their building is over 6 stories). This building was build in the 70s. I have no idea when they are going to be done.

</comment><comment><USER64> Because brick has become affordable for the common man and building techniques value speed? The average person building a house in 1915 would have a house built with wood siding because brick would have been out of his price range, even with the slave labor wages and lack of sufficient building regulations.

</comment><comment><USER65> Cinder blocks were cheaper near foundries, so a lot of plant economy homes are wood propped up and not on slabs. Slabs do not last on the "gumbo" mud, and it floods. Metals weren't cheap enough for siding so asbestos was used. Now there are the synthesized woods.

</comment><comment><USER66> What is the point of comparing a high class building with a low class building? They have not been constructed with the same budget and not to achieve the same goal. Clearly a dorm aims to lower the cost to an extreme, exactly the opposite of what a bank would do.

</comment><comment><USER67> One of the things the author brings up is that the old worksite would've had senior craftsmen - and that the standard of work of the ordinary laborer would've been higher.

Have these skilled craftsmen moved into other careers - for instance, software engineer?

</comment><comment><USER68> Is there any reason to believe that the "old" building wasn't just recently repointed? This seems like the most likely answer.

<comment><USER69> No amount of repointing could make the modern joints as even, or as narrow, as the old ones. Though to be fair I don't think the modern builders were even going for that look.

<comment><USER4> Modern builders rarely go for the tightly fitted brick look. It's possible to get brick and concrete pavers with precise dimensions and cement them tightly together, and this is common for brick and stone paving work. Walls could be made that way, but seldom are.

</comment></comment></comment><comment><USER70> Here's another question: why is the architecture in San Francisco so awful? I would take cruddy brick over hideous paneling any day.

<comment><USER71> What architecture are you speaking of? Wood buildings like the very common Victorians? I don't know what you mean by "hideous paneling," but of the many places I've lived, San Francisco has the most beautiful/interesting architecture. I grew up in a brick house on the east coast, and I find that sort of architecture drab comparatively.

<comment><USER70> Oh, no. I'm talking about stuff that's been built over the last 1 or 2 decades. Mainly, the disgusting loft buildings in SOMA and all the larger, paneled residential buildings.

<comment><USER72> It looks cheap because it is cheap. Developers have no civic pride and just want their investment to pay out ASAP.

</comment></comment></comment></comment><comment><USER73> 100 years ago, the writing engineer would never dare to have used such a narrow evidence base.

</comment><comment><USER74> Capital?

</comment><comment><USER75> Wait, aren't a lot of modern American "brick" buildings made with plywood covered with brick siding?

<comment><USER76> That is addressed in the article.

</comment></comment><comment><USER77> It is, probably, a global shift from slow and costly perfectionism to quick and cheap "good enough" (in worst possible sense of "getting shit done"). What they call a cost cutting or " optimization " is merely a form of cheating and concealing inability to and unwillingness to provide quality.

BTW, the most of buildings with have collapsed in Kathmandu around the new bus stand were these which has been built quickly with cost cutting (chap, thin steel bars, thick cheap cement layers between bricks, etc).

And this trend is everywhere, from clotches to Java. The age of getting shit done.)

</comment><comment><USER78> It may be due to the quality of the clay, or the lack of clay at all, for making the bricks. I saw a documentary on this just a few months ago aired by our local PBS station on this very subject.

[http://ninenet.org/archives/pressroom/st-louis-brick- buildin...](http://ninenet.org/archives/pressroom/st-louis-brick-building- legacy-explored-on-special-hour-long-program-2)

[https://vimeo.com/ondemand/brick](https://vimeo.com/ondemand/brick)

</comment><comment><USER79> Loginwall.

<comment><USER80> ...or you can open the web console, remove a couple of nodes from the dom, and the wall is gone. To scroll, use your up/down keys in your keyboard :)

<comment><USER81> or just disable javascript.</comment></comment></comment>


Machine learning leads mathematicians to unsolvable problem - <AUTHOR> https://www.nature.com/articles/d41586-019-00083-3 <comment><USER2> This work was published in "Nature Machine Intelligence", the journal boycotted by pretty much everyone who matters in ML.

Reflects poorly on the authors, regardless of the actual merits of their finding.

<comment><USER3> As far as I can tell, the article isn't really of any interest either.

Formulating a proposition that is independent of standard axioms is simple. Formulating it in the language of machine learn is an exercise. The main thing is the authors didn't provide any motivation for this to matter to the overall enterprise of machine learning, because there isn't motivation for this. It's just a novelty.

<comment><USER4> I don't understand your reasoning. Because, you could also "formulate" CH in the "language" of Turing machines. But that is clearly disanalogous to what the article is saying.

</comment></comment></comment><comment><USER5> One doesn't need to go back to Gödel for this to make it a "huh" moment. Instead, go back to 2006 to make it a "duh" moment.

Aggregability is NP-Hard: [https://www.google.com/url?sa=t&source=web&rct=j&url=http://...](https://www.google.com/url?sa=t&source=web&rct=j&url=http://citeseerx.ist.psu.edu/viewdoc/download%3Fdoi%3D10.1.1.78.6237%26rep%3Drep1%26type%3Dpdf&ved=2ahUKEwjg3oON9p7gAhXiHDQIHctEBfEQFjAAegQIAxAB&usg=AOvVaw3KFPsAt9iWqBpUqZrEigpu&cshid=1549174909564)

That is, even for linear systems, determining whether or not macrovariables (e.g. complete eigenvector sets, complete embeddings) exist for a given space is an NP-Hard problem. With linear systems serving as, effectively, a lower bound for ML problems (because, otherwise, why are you even ML'ing the thing?), whether or not a problem is "learnable" is, unsurprisingly, probably NP-Hard. Aggregability and learnability look staggeringly similar to me.

Demonstrating otherwise would be a _huge_ result. Writing a paper confirming Kreinovich and Shpak in a slightly different domain is basically a "Water is Wet" paper.

Having not yet read the paper, I'm unaware of any new ground here.

<comment><USER6> NP-hard and undecidability are completely different things. They're barely on the same planet.

<comment><USER7> I would argue that for practitioners it is the same planet. But I agree that they are not the same thing.

<comment><USER8> disagree, some small size NP-hard problems can be solved in practise.

or, given enough effort / luck / redefining the problem, sometimes extra structure can be found for the particular problem instances that you want to solve, meaning that they actually belong to an easier problem class that can be solved in practise -- e.g. you've got extra information or constraints that you're not actually using, so you don't need to solve the NP-hard problem in general, just solve the specific problem you've got.

i'll willing to change my position if someone can argue it is similar for undecidable problems.

<comment><USER9> Well: the halting problem is undecidable. That does not prevent us to try and prove (many many times) that an algorithm does or does not stop.

I guess the parent meant something like this.

Of course the concepts are totally dissimilar but the practical consequences are less apart.

</comment></comment></comment></comment></comment><comment><USER10> The theorem is proved for only for probability distributions with support at a finite number of points on [0,1], and the sigma-algebra of all subsets of [0,1]. This is an utterly bizarre choice and makes the whole thing basically uninteresting.

One of the first things you see in a graduate course on real analysis that covers measure theory is the construction of an unmeasurable set using the axiom of choice (equivalent to the continuum hypothesis). Then you say, "that's useless," and restrict the subsets you work with to those that don't depend on this problem, or you go work with intuitionist, finitist, ultrafinitist, or some other logic, which gives basically the same effect. Then you build all of probability theory and machine learning in this actually useful world.

The unmeasurable set construction that everyone uses is to consider all subsets of [0,1] of the form {x + r : x in [0,1], r is rational}. Since there are uncountably many irrational numbers, you end up with an uncountable number of these subsets, and then use the axiom of choice to select an element of each.

For their probability distributions with finite support, consider the sets of points that form the support of the distributions. I can form a sequence of such sets that heads towards that unmeasurable set, and a corresponding sequence of probability distributions. They completely ignore whether their set of distributions is complete (that is, contains all limits of sequences—hint, it isn't), but they're taking suprema, so they effectively are working in the closure anyway, where the limits are included.

So basically they have found an obscure way of showing the first result taught in measure theory and dressed it up in the clothes of machine learning, even though no machine learning work ever conducted or that will ever be conducted with work on this mathematical structure because of this exact reason.

<comment><USER11> This is not adding to the conversation. Your comment was my impediment in moving past the second page of the paper. Problem is, I never got to study foundations of measure theory, and presumed I could be wrong. Do you have any self-study recommendations, paper or concise books?

<comment><USER10> I really don't have a good recommendation. :( I learned it from a person, not a book, and the textbook he was assigning exercises from (Folland) is essentially useless for self study to my mind.

</comment></comment></comment><comment><USER12> Earlier discussion: [https://news.ycombinator.com/item?id=18858724](https://news.ycombinator.com/item?id=18858724) (Same research, but different news coverage)

The actual research, which I find more understandable than the news coverage: [https://www.nature.com/articles/s42256-018-0002-3](https://www.nature.com/articles/s42256-018-0002-3)

</comment><comment><USER13> Isn't all this press by the Nature publishing group just about hyping up one of its newer magazines that the larger research community is boycotting?

By the way, Paul Cohen, who proved the independence of the Continuum Hypothesis, says that Godel did not express much interest in independence results (I think Godel believed in Platonism):

[https://www.youtube.com/watch?v=VBFLWk7k1Zo](https://www.youtube.com/watch?v=VBFLWk7k1Zo)

An article by Godel, taking a philosophical viewpoint about set theory and independence, is "The modern development of the foundations of mathematics in the light of philosophy":

[http://www.marxists.org/reference/subject/philosophy/works/a...](http://www.marxists.org/reference/subject/philosophy/works/at/godel.htm)

Godel believed that for well-defined areas of mathematics, we can add more _intuitive_ axioms to make the theory decidable: The appropriate quote from the article: "I would like to point out that this intuitive grasping of ever newer axioms that are logically independent from the earlier ones, which is necessary for the solvability of all problems even within a very limited domain, agrees in principle with the Kantian conception of mathematics. "

<comment><USER14> > By the way, Paul Cohen, who proved the independence of the Continuum > Hypothesis, says that Godel did not express much interest in independence > results (I think Godel believed in Platonism):

Gödel proved the other direction of the independence of CH (and the Axiom of Choice), and had been trying to prove independence some years after that. He had actually succeeded in proving the independence of AC by 1943, and later said in an interview with Hao Wang that his methods could have probably been extended to prove the independence of CH by 1950, but he stopped working on it because he developed a distaste for the subject. In retrospect, Gödel wished that he had continued his work so that set theory progressed faster.

The article The Origins of Forcing by G. H. Moore in the proceedings of the 1986 Logic Colloquium is a good discussion of the relevant history.

> Godel believed that for well-defined areas of mathematics, we can add more > _intuitive_ axioms to make the theory decidable: The appropriate quote from > the article: "I would like to point out that this intuitive grasping of ever > newer axioms that are logically independent from the earlier ones, which is > necessary for the solvability of all problems even within a very limited > domain, agrees in principle with the Kantian conception of mathematics. "

This line of research hasn't gone very well in practice since Gödel's time. It has produced a lot of interesting set theory, but has not really impacted mathematics at large.

<comment><USER13> Thank you for the reference on forcing. Will read it carefully.

> This line of research hasn't gone very well in practice since Gödel's time. > It has produced a lot of interesting set theory, but has not really impacted > mathematics at large.

What about Hugh Woodin's work? I agree that it has not had impact yet, but do you think it might lead along this suggested line?

</comment></comment></comment><comment><USER15> _" In the latest paper, Yehudayoff and his collaborators define learnability as the ability to make predictions about a large data set by sampling a small number of data points. The link with Cantor's problem is that there are infinitely many ways of choosing the smaller set, but the size of that infinity is unknown."_

Reading this got me wondering about more philosophical aspects, such as the relation of this conclusion to to the process of human learning and prediction (which obviously works) and whether it's somehow tied in some way to the problem of induction. Could be nonsense, but I'll be putting some more thought into the meaning of this

<comment><USER16> The problem with these papers is, that if you want to do practical ML, you can simply fix some upper bounds on various numbers that arise during the analysis of the problem, and thus make it mathematically finite, and trivial. Not easy, of course, but this frees you from the infinite regress that's the problem of induction.

Sure, you can the start to ask what are the good upper bounds. How many epochs to use for training, start to quantify the training set quality, and then ask how good that must be to get a good enough model. Etc. But all of these then can be limited by estimation.

</comment></comment><comment><USER17> Not completely on the subject, but I had to read the first sentence 5 times, before I was able to understand its meaning. Then I realized it was too long, so modified it to following version. Is it better or worse?

"A team of researchers has stumbled on a question that is mathematically unanswerable. It is linked to logical paradoxes, that were discovered by Austrian mathematician Kurt Gödel in the 1930s and it can't be solved using standard mathematics."

<comment><USER18> Yeah, it's a bit better. Not sure how much, maybe more for non native speakers?

<comment><USER17> Thanks! English is my 3rd language, so I do struggle with reading sometimes.

</comment></comment></comment><comment><USER19> If I understood the article correctly (and I think I didn't) it says learnability of a given data-set is like the halting problem, there is no general algorithm for deciding whether an arbitrary data-set is learnable. Am I close?

<comment><USER20> This was my takeaway from the article as well. Even though I have no academic knowledge on the subject, can't say I was surprised to learn this. To me it seems obvious in hindsight, though might be Dunning-Kruger.

</comment></comment><comment><USER21> Can someone explain why/if this is a big deal? It seems to me that they just rehashed undecidability and logical incompleteness.

</comment><comment><USER22> I don't understand how a result concerning infinities can apply to a finite number of data points represented by finite (bounded - probably by 2^32) integers processed in finite time.

<comment><USER23> The reals are infinite. Float/double

So, while I think your question is interesting and good, I don't think integer size is a strong counterexample in support of a different conclusion.

<comment><USER24> float/double can store a subset of the rationals plus some other values which aren't found in the reals

<comment><USER25> And those other values are finite (NaNs, infinities, unequal zeros). I don't know why you're downvoted. What you said is absolutely correct.

It's an absurd thing for GP to say integers aren't infinite (apparently talking about fixed width integer types) and then turn around and say float/double are infinite (talking about single precision and double precision floating point types).

</comment></comment></comment></comment><comment><USER26> Question for someone with a more theoretical background: The paper shows that the EMX learnability of some class of functions with respect to some set of probability distributions is undecidable. Does EMX learnability encompass all notions of learnability (or is it equivalent to other notions)? Conversely are there or could there be notions of learnability different from EMX that are not undecidable? Maybe I missed this in the paper but clarification would be appreciated.

</comment><comment><USER27> I mean, c'mon we all saw this coming...

</comment><comment><USER28> Where is mathematics in ML today? Most of that are happening under the hood and all algorithms are just a black box.

<comment><USER29> There's a very neat and often forgotten piece of math in learning, VC dimension (unrelated to venture capital):

[https://en.m.wikipedia.org/wiki/Vapnik–Chervonenkis_dimensio...](https://en.m.wikipedia.org/wiki/Vapnik–Chervonenkis_dimension)

Also, the reason why black box methods are such a big deal now is precisely because controlled/engineered methods turned out to be inferior (obvious example: image recognition; look no further than into the story of the dropout method and Alex Krizhevsky).

Edit: s/basically forgotten/often forgotten/ in the first sentence.

<comment><USER30> It's not very forgotten if it's in the Learning from Data course, to say the least

</comment></comment></comment><comment><USER31> Professor Peter O'Hearn (UCL Computer Science) says latest research findings on 'unsolvable' mathematical problems is "of a rare kind", and will probably be important for the theory of machine learning.</comment>


22 Dream Jobs Way, Way Out of the Office - <AUTHOR> http://www.atlasobscura.com/articles/the-great-escape-job-board

<comment><USER2> not sure about the rest of you, but none of these are dream jobs... I'd give myself 6 months before I get bored :D</comment>


How Birth Season Affects Personality - <AUTHOR> http://www.theatlantic.com/national/archive/2014/10/how-birth-season-affects-mood/381727/

<comment><USER2> Single study, self-administered questionnaire, not a lot of variation in the sample, and not a huge sample size to begin with. Meh.</comment>


Space shuttle Discovery landing  - <AUTHOR> http://www.youtube.com/watch?v=22-Ji8_kDwg&fmt=22

<comment><USER2> Here's a shortcut to what we're all really interested in :)

[http://www.youtube.com/watch?v=22-Ji8_kDwg&fmt=22#t=2m55...](http://www.youtube.com/watch?v=22-Ji8_kDwg&fmt=22#t=2m55s)</comment>


Barr's crypto backdoor claim is a fallacy, which I'll show with math - <AUTHOR> https://twitter.com/ErrataRob/status/1154473459247828992 <comment><USER2> A lot of people here commenting on how Barr won't care/etc. I don't see that as the point for this discussion.

In my view; If "we"[1] are to win, these types of information sharing/etc posts are essential. As commenters have pointed out, Barr won't care about this logic. In fact, there is no logic that Barr and his ilk will care about. Yet there are hundreds of thousands of people who simply have no idea. They are not uncaring or malicious, crypto is a complex topic and they're not computer people. Barr and his group will _(and have!)_ spin crypto to be something terrorists and pedophiles solely use to get away with evil. We need to have equal, if not greater, "counter spin" to at least combat the propaganda.

Call it educating the public or call it propaganda, it doesn't matter. We may not win if we publish articles like this, but we will certainly lose if "we" are the only ones that care about this topic. When the game is played on such a large scale we can't depend on people being informed, we need to bring people information.

I don't intend to discuss how effective information on this subject will be to the "common" person; but I think we need to try. Lest we lose crypto with thunderous applause.

[1]: People who care about crypto and privacy/etc.

 _edit_ : Many typos. Coffee, save me.

</comment><comment><USER3> Barr and others like him have been saying this stuff for decades. Showing them the math has limited utility. Geeks have been doing that for decades too, with limited results. Barr and his predecessors don't read math, they wouldn't understand it if they did, and even if they understood it, they would demand backdoors anyway. Barr in particular has already demonstrated that national security and our economy are less important to him than increased power. It's probably true of all these government people making all these false claims about cryptography since the mid 1990s, but it's demonstrably true of Barr. (The Trump coverup he's currently attempting is not even his first coverup as Attorney General. He did similar work for a previous administration.)

</comment><comment><USER4> Math won't change his mind (or other politicians). I think they already know what they can do with a backdoor and why it is bad. I don't think they care.

</comment><comment><USER5> There are other means of backdooring rather than setting key size.

I'm not saying its a good idea, but there are means to make cryptosystems that are breakable by the NSA but not anyone else. Consider the concerns around the Dual_EC random number generator that was pushed by the NSA. People believe that the NSA has a backdoor into that random number generator due to how the constants were generated. There are similar concerns for various ECC curves.

So the government could mandate that industry uses their specific RNG or specific ECC curves. Effectively giving them a backdoor that nobody else has.

It's disingenuous to argue its a bad idea because its impossible to build. It's also a bad argument strategy, as once someone learns that it can be built they will assume that you're lying to push your agenda and not trust further arguments you put forward.

<comment><USER6> > Effectively giving them a backdoor that nobody else has.

Until they do...then you go from 100% to 0% as TFA states.

All it takes is someone figuring out how the NSA generated their magic constants (which obviously contain a flaw) and its game over.

<comment><USER5> Sure but that's not the argument that the article made. Thats an important point to discuss and there may be ways to mitigate the damage of such a compromise (multiple curves, per key escrow). The article made a ridiculous argument for why backdooring is "impossible". Presumably they made it to persuade laypeople but what they really did is misinform laypeople and set them up to be pushed to the other side when they find they've been lied to.

Not to mention you're also fucked if an unintentional flaw is discovered in AES or similar. You still need to be able to upgrade you crypto in response to advances in the state of the art, or leakage of important secrets.

</comment></comment></comment><comment><USER7> I see the focus on practicality as a bit misguided. Even if it could be done, giving the government (and its friends) covert access to all information is dystopian.

Looking at the recent history of pretty much any country (including the US, let alone Russia or China, or North Korea) should show what a terrible idea this is.

Edit: It wouldn't even improve safety. Imagine how convenient it would be for the military-industrial-prison complex to know everything about every anti-war activist. The increased oppressive capacity would more than make up for any decrease in crime.

That's all assuming Americans have turned fully utilitarian, and discarded any pesky ideals such as 'freedom' that might further tilt this analysis.

</comment><comment><USER8> "Keys Under Doormats" should be required reading on the issue of exceptional access. [https://www.schneier.com/academic/paperfiles/paper-keys- unde...](https://www.schneier.com/academic/paperfiles/paper-keys-under- doormats-CSAIL.pdf)

tl;dr Governments are vague about what they actually require in terms of exceptional access. And few ever discuss how to mitigate the inevitable multi- jurisdiction conflicts, like if China compels Apple to unlock phones belonging to US-friendly intelligence assets.</comment>


Despite Everything, America Remains a Nation of Hot Dogs - <AUTHOR> https://www.citylab.com/life/2019/07/hot-dog-eating-contest-july-4th-usa-bbq-photos/593305/ <comment><USER2> Schonland's hot dogs (the kind you see in cartoons that link together) on New England hot dog rolls (square, stand up, white on the sides, buttered and toasted)...are a thing of beauty. Sooooo good. I honestly don't care if they are made of offensive pig parts, or if they are terrible for me. A little spicy mustard and relish...yumm. I'd honestly trade some life expectancy for living good.

A visual, if you've never had one: [https://cdn1-vcxkoqvocaf7mso0.netdna- ssl.com/wp-content/uplo...](https://cdn1-vcxkoqvocaf7mso0.netdna-ssl.com/wp- content/uploads/2015/08/Screen-Shot-2015-08-04-at-7.53.51-PM.png)

</comment><comment><USER3> I'll take my pizza NY-style over that crazy deep dish cheese tomato sauce casserole thing they serve in Chicago any day, but a Chicago-style dog definitely tops a NY dog, no question about it.</comment>


Jerry Lawson helped lay the groundwork for all modern gaming consoles - <AUTHOR> http://arstechnica.com/gaming/2016/02/you-wouldnt-be-able-to-pause-your-video-games-today-without-jerry-lawson/ <comment><USER2> A few highlights: Black engineer in Silicon Valley. In 1970. _Demolition Derby_ released months after _Pong_. Fairchild Channel F console had programmable cartidges and real game AI. Want to know more.

</comment><comment><USER3> Interesting that Lawson "wasn't very impressed" with Wozniak (or Jobs) when he applied for a job. I'm not clear on the timing, but it sounds like this would have been after they built Breakout for Atari.

</comment><comment><USER4> These kinds of stories annoy me to no end. This guy happens to black, so therefore we must celebrate him?

How about just celebrating him for what he did. Who cares about his skin pegmentation?

<comment><USER5> Because he did those things while playing on the 'hard' life difficulty setting.

At any rate, you're presenting a false dichotomy. It's not an either/or proposition. They -are- celebrating what he did; it's all the more impressive that he did it while being black, in a time and place where that was a major obstacle.

<comment><USER4> He lived in the exact right place for this though. From my point of view he was privileged.

A lot of e.g. white western Europeans would have spent a lot of money to get into this position.

(Note: I am not advocating a handicap system for Europeans! :) )

<comment><USER5> I bet he would have spent a lot of money to get into that position too. Except he and his family were of very limited means.

Really, if you want to play the "other people have it harder" game, I will readily bow out; of course there are.

But within the confines of "here's someone who had a major influence in his profession", to dismiss his skin color as not being of note, to ignore the additional obstacles society would have placed in front of him, is to deny him some credit for having overcome those obstacles. That's why it's mentioned, that's why it matters. I agree, ideally it wouldn't matter; the fact is is that because to some people being black is a detriment means that being black includes extra obstacles, and it's worth recognizing those who overcome them.

<comment><USER4> You seem really intent on not getting my point.

My point is that for this particular thing, location is of supreme importance. Skin color is really, really far down on the list.</comment></comment></comment></comment></comment>


Drill Down HN : Github - <AUTHOR>

When I land at web apps or sites upvoted here in HN, most of the time I wonder - how these sites were developed. Figuring out all architectural, technical and UI aspects of an app or a site would be inspiring to a developer-cum-lurker like me.<p>Shall we start with http://github.com <comment><USER2> GitHub itself provides quite a bit of information about their internals over at their blog: <http://github.com/blog>.

A few I found interesting:

* <https://github.com/blog/517-unicorn>

* <https://github.com/blog/542-introducing-resque>

You also might want to check out their public projects: <http://github.com/github>

Or those of the founders:

* <https://github.com/mojombo>

* <https://github.com/defunkt>

* <https://github.com/pjhyett></comment>


Self-Replicating Functions - <AUTHOR> http://tylerneylon.com/a/self_repl/ <comment><USER2> That is a beautifully typeset article.

<comment><AUTHOR> Thanks! I'm considering writing a follow-up note on the process that went into the typesetting. The original source is a markdown-with-latex format that a tool called pandoc can work with. The style is primarily from tufte.css. The image work is mostly custom, but there are some re-usable approaches. If you're curious:

[https://github.com/tylerneylon/math/blob/master/self_repl_fn...](https://github.com/tylerneylon/math/blob/master/self_repl_fns/self_repl_fns.md)

<comment><USER3> fyi: the numbered lists only take up half the width of the normal paragraphs, making it look a bit janky and odd, on my chrome on OSX.

</comment></comment></comment><comment><USER4> My favorite self-replicating function is the sine, and I spent some time finding it using just its very strong self-replication properties here:

[https://myownfortune.wordpress.com/2017/09/21/why-sine- wave/](https://myownfortune.wordpress.com/2017/09/21/why-sine-wave/)

<comment><USER5> By the way, this is a nice article, but you unfortunately mix up "frequency" and "period" in your quantitative discussion. (A function that repeats every 50 units, for example, has a period of 50 units, as opposed to a frequency of 1/50 1/units.)

</comment></comment><comment><USER6> This is a fun exploration! It's interesting that the summed functions have a feature topology that mirrors each sub-function, but some of the local features retain their original scaling, while features in the overlap region adopt a new scaling. This reminds me a little of using absolute scaling in SVG or CSS on something that is parented or embedded (not at the root of the hierarchy). Sometimes you use that kind of thing for character rigs in movies & games - break out of the local coordinate system and use world space.

Since the scaling isn't uniform, this is what causes t1 & t2 to have to be piece-wise linear. I'd love to see what happens if the transform functions, i.e. t1 & t2, were restricted to affine transforms. Like, how much harder is it if you further require the summed function to be a uniformly scaled & translated version of the sub-function? What if you added to the formal definition something like: f_S = a * f_L ( b * x + c ), where a,b,c are constants

This also reminds me of a mutation I added to my artificial evolution digital art project where I was trying to generalize on the idea of a fractal. I called it the 'harmonic mutation', and it takes any function f(x) and produces a new function with two or more scaled copies, like c0 * f(c1 * x + c2) + c3 * f(c4 * x + c5). Repeat several times with the same constants, and you can make a fractal out of any function at all. Very similar concept to Perlin turbulence too, where you have summed & scaled octaves of noise.

<comment><AUTHOR> Cool connections. Do you happen to have a link for the digital art project?

<comment><USER6> Of course. ;) I elaborated on harmonic mutations in a paper here: [http://dahart.com/paper/hart_evomusart_2007_paper.pdf](http://dahart.com/paper/hart_evomusart_2007_paper.pdf) and there's a gallery of images on Flickr: [https://www.flickr.com/photos/biv4b/albums/576553](https://www.flickr.com/photos/biv4b/albums/576553)

<comment><USER7> Congratulations, really cool and innovative! Have you looked into ArtMatic and how you can create a tree of functions ? It allows to create mutations that give results very similar to yours.

<comment><USER6> I hadn't before, thanks for the tip! It's been a while since I played with this stuff, but I might have to get a copy and explore. I have heard of MetaSynth in audio circles. I'm not sure, but the images and videos on the ArtMatic site look (to me) very inspired and influenced by the work of Karl Sims, which is the main source of inspiration behind my project... [http://www.karlsims.com/papers/siggraph91.html](http://www.karlsims.com/papers/siggraph91.html)

You can find a bunch of his videos on YouTube too.

[https://youtu.be/AgeuRukfZLE](https://youtu.be/AgeuRukfZLE) [https://youtu.be/vIVjEkWTEXI](https://youtu.be/vIVjEkWTEXI) [https://youtu.be/SLAa-CnUEW4](https://youtu.be/SLAa-CnUEW4) [https://youtu.be/JBgG_VSP7f8](https://youtu.be/JBgG_VSP7f8)

<comment><USER7> Thank you for the link to the article! I know Eric Wenger the author of MetaSynth / ArtMatic / Voyager since many years and his motivation to create ArtMatic was to create textures to feed MetaSynth to create music from visuals..

</comment></comment></comment></comment></comment></comment><comment><USER8> Refinable functions, used for constructing wavelets and subdivision schemes, seem similar: [https://en.wikipedia.org/wiki/Refinable_function](https://en.wikipedia.org/wiki/Refinable_function) and [https://arxiv.org/abs/1012.2453](https://arxiv.org/abs/1012.2453)

</comment><comment><USER9> The definition of an exactly self replicating function seems to be any function 'f' such that there are continuous bijections a,b,c such that f∘a + f∘b = c∘f, and a does not equal b.

Edit: I think this includes all strictly quasi-concave functions, but I'm not entirely sure.

<comment><AUTHOR> I think you're right. Your version of the definition is more elegantly stated, and I may want to use it going forward, as long as a, b, and c still make intuitive sense (thinking about that part).

<comment><USER9> Feel free to use it. Using your notation you have a=t1, b=t1∘s, c=t2^-1. Inversely you have s=a^-1∘b, t1=a, t2=c^-1.

</comment></comment></comment><comment><USER10> Just if anyone interested: There are also sequences that are labelled 'fractal', those are fun too:

[https://oeis.org/A000120](https://oeis.org/A000120)

 _' An example of a fractal sequence. That is, if you omit every other number in the sequence, you get the original sequence. And of course this can be repeated. So if you form the sequence a(0 _ 2^n), a(1 * 2^n), a(2 * 2^n), a(3 * 2^n), ... (for any integer n > 0), you get the original sequence.' _

</comment><comment><USER11> When I saw Figure 3 I was reminded of the New Zealand kidney fern, where the veining is a very close approximation to that type of L-system, at least for the first seven or so divisions. [http://www.terrain.net.nz/friends-of-te- henui-group/nz-ferns...](http://www.terrain.net.nz/friends-of-te-henui- group/nz-ferns/kidney-fern.html)

<comment><USER12> You might also be interested in the monkey puzzle tree.

<comment><USER13> [https://en.wikipedia.org/wiki/Araucaria_araucana](https://en.wikipedia.org/wiki/Araucaria_araucana)

It is indeed interesting.

</comment></comment></comment><comment><USER14> Based on the title, I imagined this would be about AWS Lambda functions.

I wonder if anyone tried simulating evolution using these. I suppose you could even make the fitness be about earning money, e.g. solving captchas? Such that if a function can't pay for its own upkeep it'd die off, while if it does well it could spawn offspring.

</comment><comment><USER15> What software did you use to create your figures? They look great.

<comment><AUTHOR> Thanks! The original source is custom js rendering to svg. The html version of the article contains png files based on that output; the pdf version contains vectorized versions. I got some solid design input from Mike Sall on the images for this article.

Edit: example: [https://github.com/tylerneylon/math/blob/master/self_repl_fn...](https://github.com/tylerneylon/math/blob/master/self_repl_fns/images/scratch/nonlinear_ramps.html)

</comment></comment><comment><USER16> This reminds me of the concept of a "ring of functions" (albeit slightly more constrained). Since you seem to be familiar with measure theory already, that idea is probably already well known to you (the author), but I figured I'd mention it anyway.

<comment><AUTHOR> I didn't know about that before. Looks very interesting (looking at wikipedia) — thanks for mentioning it!

<comment><USER16> I highly recommend learning abstract algebra thoroughly if you haven't already, by the way. It's a lot more well connected and well researched than you might think after just reading about this or that definition (groups, rings, quotient rings, lattice of ideals) in a vacuum. The magic comes when you mix all the definitions together. If you learn it correctly and master both the rigour and intuition behind it all, you'll come to consider your pre- abstract-algebra-self in the same Platonic cave as you might see your pre- linear-algebra-self right now.

</comment></comment></comment><comment><USER17> A while ago I thought about the fact that if you repeatedly apply f(x)=2+x/2 to a number, you approach 4. What happens if you repeatedly apply, with a 50/50 chance, either x/2 or x+2 to a distribution? What distribution do you get?

I could find a lot of analysis using matrices in discrete math, but I couldn't find much for continuous distributions. I haven't gotten all the way through reading this, but it seems like it could be helpful.

<comment><USER5> This sounds quite a bit like a probabilistic version of the Collatz problem ([https://en.wikipedia.org/wiki/Collatz_conjecture](https://en.wikipedia.org/wiki/Collatz_conjecture)). I thought I'd seen results on this before, but a quick Google result doesn't turn anything up. (Instead, Google results want to discuss probabilistic heuristics for why the deterministic Collatz conjecture holds.)

<comment><USER17> Hmm. Thanks for the thought. I'm not sure how related it is, but I might find something in the attempted solutions.

The original idea behind this was to figure out how to study the stability of certain probabilistic transformations. The hope was to be able to make transformations that are good at detecting non-random inputs, particularly in time-series data. Could potentially be used in a similar way to neural-nets.

</comment></comment></comment><comment><USER18> Nice post!

If you're interested in future directions, or working off of research that others might have generated while looking into similar questions, for the sake of taking this idea (self-replicat'n functions) to that next level.. it would be p interesting if you could use just a hint of the much-fabled _category theory_ for the sake of generalization!

</comment><comment><USER19> hm, now I wonder what happens if you take 'any old function', add it to a reversed and shifted version of itself, and normalize. do you eventually get one of these self-replicating functions, or are there functions that 'diverge' under this treatment?

Taking a random array and giving it this treatment, I seem to get a gaussian distribution after just a few (say, 100) iterations on a 100-element sequence, shifted by 1/3 and then downsampled to be a 100-element sequence again). but of course this is a global and downsampled view, the function might be very craggy locally.

</comment><comment><USER20> lovely class of functions, is it part of a math domain of research ?

<comment><AUTHOR> This is independent work. Probably fits in with fractals and L-systems.

<comment><USER20> So that was all you had in mind as a starting point ?

again, lovely article, got inspired by ti

<comment><AUTHOR> That's all the solid work I have so far. Tons of ideas for what could be next. For example, consider convolutions on sets generated by L-systems (eg the Cantor set). I suspect those might offer continuous, finitely-supported, linearly-shifted self-replicating fns (the current article is mainly about non-linear shifts; t_1 is only piecewise linear). Maybe L-systems even completely characterize that category of self-replicating fns.

Other ideas: * Higher dimensions (eg f1 + f2 + f3 = g with domain R^2) * Shifted fns f1, f2 whose sum has surprisingly small diff from their sum: ie small |C(f1+f2)-shift(f1)|; the normal fn appears to fall into this category

<comment><USER20> as in elf similarity across projection, a R^n composition that ends up a as a function on R^N-1 ?

</comment></comment></comment></comment></comment><comment><USER21> His first examples g1, g2 are not shifts of f. What am I missing.

<comment><AUTHOR> You're right that the g1 and g2 in section 2 are also scaled in addition to being shifts of f. I plan to clarify this in the text.

This work is inspired by the self-similarity of fractals, which is in some cases primarily an intuitive or informal idea: for example, the Mandelbrot set is considered self-similar, but I'm not aware (despite searching) of any simple automorphisms of the Mandelbrot.

<comment><USER22> There's this local example in Wikipedia: [https://en.wikipedia.org/wiki/Mandelbrot_set#/media/File:Man...](https://en.wikipedia.org/wiki/Mandelbrot_set#/media/File:Mandelbrot_zoom.gif)

</comment></comment></comment><comment><USER23> Articles like this make me so sad, because it seems absolutely fascinating, but I know nothing about math. I became a programmer later in life and never got a solid education in it.

Beautiful visuals though, lol.</comment>


Ask HN: How do you see life changing after the coronavirus? - <AUTHOR> <comment><USER2> My naive predictions:

\- Countries are going to become increasingly authoritarian, not unlike what happened after the Great Depression

\- There are going to be a lot of angry poor people looking for someone to blame and they might become violent; there might be riots, protests, or calls for revolution

\- There might be a slight increase in abortions or births depending on the current prudence of couples

\- Some countries might start experimenting with permanent Universal Basic Income once they realize how unnecessary most jobs have become

\- Mental health and self-esteem is going to degrade (esp. in the younger generation); there might be a sharp increase in suicides or people who choose to opt out and become recluses

\- We will see a very strong push towards smart cities, cybernetics, and eugenics by the start of the next decade

\- Leaks upon leaks of nude media from all the random sexting going on during the quarantine

\- Plenty of divorces

</comment><comment><USER3> Following the great depression, the generation that had lived through those trying times was extremely frugal, known to keep gold and cash in matresses and other furniture. I expect that this virus will deeply affect the frugality of those living through this in a similar matter. Millions upon millions of people are out of work for an unknown amount of time. At least in the US, a massive proportion of the population couldn't even pay an unexpected $1000 expense before this.

</comment><comment><USER4> the millenials+younger will revolt against the rent-extracting policies and regulations set by the previous ones</comment>


What are the best ways for building critical mass of a new q&a site? - <AUTHOR> http://wisd.io/-Mj7t Any other good ideas? <comment><USER2> Make Mike Arrington wanna use it. Or Scoble, at least ;)

<comment><AUTHOR> Sure I will!</comment></comment>


Show HN: Slicer for OS X - <AUTHOR>

Here's my new Window Management app for OS X (think SizeUp, MercuryMover, Shift-It, etc).  Mine uses a "recursive" style of interface that always starts a window Full Screen and then cuts in it half (or thirds) with each keypress.  Works with dual monitor rigs and is fun to use.
Please kick the tires:
http://allsystemsgrow.com/slicer/Slicer.zip
Demo video:
http://www.youtube.com/watch?feature=player_embedded&v=_u7nvEWjZuk#!
Let me know what you think! <comment><USER2> This is pretty well done. I'd like it better if I could use it with just my left hand. I use an external mouse and keyboard - I'd prefer to not have to take my right hand off the mouse.

I've been using Flexiglass for a while now, but only really the ability to drag a window to an edge of the screen and have it size it accordingly (top is full screen, sides are vertical half, corners are quarters, etc)

</comment><comment><USER3> Thanks! I played with it and thought it was pretty cool. Will let you know after a few days to usage. Shoot me an email with your contact (in my profile).

<comment><USER3> I'm not sure if this was by design for if there is a bug but on multiple monitors, at times, the window would shift completely to the other screen. So far, that, and sometimes the window seems to move out of alignment from the edge are the only issues I've encountered. But otherwise an awesome tool.</comment></comment>