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18:00
well I smoke
:(
is that evil?
Yup, and not good for you.
But I wasn't talking to you about it, so it's OK, I suppose.
now that I'm taking a break semester, I have time to do some other things. Meet up with friends a lot, learn French and Japanese
Heya, @Semiclassic. Back from your vacation in Italy? :P
@TedShifrin Let me rephrase it then. "well, I smoke too"
18:01
yeah
@MatheinBoulomenos A language nerd, eh
Italy+London, really
That's great, @Mathein. I still need to learn Spanish. My French is more than adequate.
didn't see a lot of Italy---conference site was a small Italian town---but what I saw was distinctive
how old are you guys
18:02
@Ted It's the least I can do for the world, die quicker
lot of walking on old cobblestone roads
London was more than just passing through the airport, @Semiclassic?
Nah, a @Balarka.
yeah, and deliberately so
I spent a few days there after the conference
le francais est tres difficile
18:02
Geogebra is a free graphing tool I play with sometimes, Sub, if you're looking for something prettier than ms paint
Great. Too bad you didn't stay for the protests now. :P
@Semiclassical Italy has a lot of those right
@BalarkaSen well, that's definitely not the right mindset.
Oh, where were you in Italy?
18:02
@BalarkaSen ya
@AlessandroCodenotti Viterbo
Pas du tout, @Mathein, moins difficile que l'allemand.
Not very well-known, I think
The crazy Italian driver's ears perk up at "cobblestone roads"
hey there, demonic @Alessandro
Never been there
18:03
eta ki language vai
l'italiano è più facile che il Francese
yes, Alessandro is still trying to run me over.
@SubhasisBiswas French
18:03
hey @Mathein!
hey @ÍgjøgnumMeg @LeakyNun
@MatheinBoulomenos long time no see
Shit everyone's here
heya @LeakyNun boi
I had a bit of an altercation with an arrogant SOB on main, eventually flagged his second set of insulting remarks and somebody removed them.
18:04
wow, that's kind of a reunion
@Mathein how ya doing, long time no see :)
oh, hey there @Leaky.
I spent Thursday evening - Sunday morning in Italy, then flew back to London and spent the rest of the week there
oh, and @ÍgjøgnumMeg too.
Hi @Leaky, @ÍgjøgnumMeg
18:04
@ÍgjøgnumMeg I wasn't doing great for a while, but I'm doing better now
@MatheinBoulomenos did I tell you I'm learning knot theory now?
you did knot
@Mathein glad to hear it! :)
He's knot learning any theory
smacks Mathein for old times' sake
18:05
I got to see Bletchley Park which was neat
You make that joke far too often Ted
oh, cool, @Semiclassic.
@BalarkaSen oof
yeah
one name I didn't really know about in connection with that: Bill Tutte
I am the proprietor of uncreative puns.
18:05
@Mathein I'm coming to Heidelberg finally.. hahaha
@ÍgjøgnumMeg I'm looking forward to it
@MatheinBoulomenos I was reading your proof of $\pi_1(S^1)=\Bbb Z$ the other day
I don't know the name, either. Sadly, I didn't hold on to Andrew Hodges' fabulous biography.
shipping you two
18:06
I'd heard the name before, but I didn't connect that he was involved with Bletchley Park activities
@LeakyNun oh yeah I messed up the reasoning for homology = cohomology I think
do you have a refined proof?
@TedShifrin past WW2, he's known for contributions to graph theory
Lol he immediately remembers it
18:07
read it as a proof for $H^1(S^1)=\Bbb Z$ if you want
web.math.ucsb.edu/~cmart07/vector%20calc%20review.pdf Any links/books/repositories of more problem like this?
I also did a train trip during the day to visit the church where TS Eliot's ashes are, though the building itself was closed (it's a parish church, not a tourist location)
is it okay if I skip the first chapter of Artin?
18:08
I wrote lots of interesting/challenging problems in my multivariable math book, @Ajay, but they're not posted on line.
@Semiclassical Oh nice
I went through it
@BalarkaSen yeah
Was it a Wednesday? :)
hmm. I think it was, actually
18:09
Damn
haha
though Ash Wednesday was a while ago now
I now have an idea how permutation matrices work, computations, and an intuitive idea of a matrix operation. Is it okay now to start working my way through the group theory from artin @BalarkaSen
Sat on a bench in the churchyard---next to some very old graves---and read a few of his poems through
East Coker for one (obviously, since that's where the church is)
18:10
you need to prove that $H^1(S^1)$ is torsion-free (it's clear that it's finitely generated). Note that $\pi_n(S^1) = 0$ for $n\geq 2$ by the covering $\Bbb R \to S^1$ and LES of homotopy groups for fibrations, so that $S^1 = K(\pi_1(S^1),1)=K(H_1(S^1),1))$ (by Hurewicz + $\pi_1$ of top. groups is abelian). If there was any torsion in $\pi_1(S^1)=H_1(S^1)$, then the cohomological dimension of $\pi_1(S^1)$ would be infinite,
contradicting the fact that it is finite since $S^1$ is a finite-dimensional manifold
I kept returning to East Coker throughout this semester in college at various times
@BalarkaSen oh, nice
Virtually returning?
@LeakyNun that should fix it
nice to bring some group cohomology into the mix as well
I wish I had been able to spend a little while longer there, but I got delayed in getting there and didn't want to be paranoid about catching the train back
18:11
@MatheinBoulomenos I did that argument.
@Mathein: You haven't lost too many steps in your absence :)
@BalarkaSen nice
@TedShifrin Yes, I see. I’ve found just your linear algebra text, not of MVC. Do you know of any other source?
May 29 at 19:23, by Balarka Sen
I suspect what Mathein, that crazy man, did was that he didn't want to compute $H_1(S^1)$ by hand, so he argued that since $\pi_1(S^1)$ is abelian, it can't have torsion, because otherwise $K(\pi_1(S^1), 1)$ is infinite dimensional, but $K(\pi_1(S^1), 1) = S^1$ because it's universal cover is $\Bbb R$ which is contractible. So now $H_1(S^1)$ is torsion-free, hence by UCT $H_1(S^1) = H^1(S^1)$, and then he extracted off $H^1(S^1)$ from etale cohomology
I know you too well
you do indeed, my dude
18:12
Wait is the semester already over in Heidelberg?
There are standard multivariable calculus texts, @Ajay. Marsden & Tromba, Colley, Williamson, Crowell & Trotter, and I'm sure plenty more.
no, I'm taking a break semester
@TedShifrin I guess :)
Ahhh
Makes sense
@Balarka: Here's an odd question.
18:14
@MatheinBoulomenos I have a question for you. If $G, H$ are simplicial groups and $f : G \to H$ is a morphism of simplicial groups such that $f[n] : G[n] \to H[n]$ is surjective, is that enough to guarantee $f$ is a Kan fibration? I think so
hmm, given all the people that are here, a historical question: The set of real random variables with finite second moment forms a real vector space. Moreover, this vector space is equipped with inner product $E[XY]-E[X]E[Y]$.
How far back does this construction go?
Never seen it before, @Semiclassic, so I'm out.
@TedShifrin I was searching just a problem book. Thanks for the suggestions though.
Earliest reference I know to it is a 1937 paper by de Finetti
@TedShifrin Interesting.
18:15
@TedShifrin it's the covariance
Yes, @Leaky, so I see, but I've never seen the abstract interpretation before.
I'm a newbie on probability.
that's how you prove that correlation is bounded by 1
by using Cauchy-Schwarz
@BalarkaSen sounds reasonable, but not sure
so that sets a bound on the correlation between random variables X and Y. de Finetti remarked on that, but further asked: If you know the correlation between X and Y, and the correlation between Y and Z, does that bound the correlation between X and Z?
(Pearson correlation, to be precise)
Geometrically, the point is that---if you understand X,Y,Z in this vectorial way---then these three correlations are just the three direction cosines between X,Y, and Z.
18:18
@MatheinBoulomenos imagine a continuous injective map $f:[0,1]\to\Bbb R^3$ whose complement isn't simply connected
sounds quite weird
So you can say stuff like: The angle between X&Z can't be larger than the angles between X&Y and Y&Z, and the sum of the three angles can't exceed 360 degrees
@Semiclassic: I think I sent you the MA thesis on the linear algebra/geometry of statistics that I co-directed. Erik discussed a bunch of this stuff in there.
and that yields inequalities on the pairwise correlations
@TedShifrin hmm, I think you're right
He also has some historical remarks, as I recall.
18:21
yeah, Erik Jacobson
@TedShifrin If you think of random variables as measurable functions on some probability measure space, this is almost the L^2 inner product on the subspace square-integrable random variables (i.e., those with finite second moment), if you like.
Rather, E(XY) is the L^2 inner product
Upto scaling, I guess you quotient by the degenerate random variables
Sure, I get it, @Balarka.
Well well well who do we have here?
A lot of nerds
18:23
also, if you take the norm induced by the covariance, then the length of a vector is just its standard deviation
@Daminark hi
and the distance between two vectors is $\sigma(X-Y)^2$. that's zero when $X-Y$ is a degenerate r.v., which is what Balarka has in mind I think?
The Balarka-Alessandro message sequence reminds me of the first 8 seconds of this: youtube.com/watch?v=5oZi-wYarDs
But yeah how are you guys doing?
livin' the dream
18:24
@Semiclassical Yeah.
Nice
(Which dream?)
hi Demonark
in particular it means that there's no distance between X and X-E[X]. So while I'd insist on the inner product being E[XY]-E[X]E[Y], in practice there's no harm
the dream where I work a soul destroying job for 4 more months :(
@ÍgjøgnumMeg: Think of it as further motivation to work your butt off in grad school.
18:25
@Ted Yeah I totally will hahaha
actually I'm contractually obliged to work my butt off
since you can assume wlog that you've picked random variables with zero mean
That is the exact phrasing of the contract
hahaha
the holder will work his or her butt off
@Daminark Good movie, and good meme
@LeakyNun consider $\Bbb R^3 \subset S^3$, let $X$ be the image of $[0,1]$ under your continuous injective map, let $Y=[0,1] \cup \{\infty\}$ so that $\Bbb R^3 \setminus X = S^3 \setminus Y$, then by Alexander duality $H_1(S^3 \setminus Y)=H^1(Y)=0$, so that even if $\pi_1(\Bbb R^3 \setminus X)$ is non-trivial, it has trivial abelianization
18:27
@ÍgjøgnumMeg The Hölder?
@MatheinBoulomenos Correct
Moving to less abstract matters of probability, I've been thinking about the following lately
Even Balarka's puns are analysis-based now. Once he says the word "distribution" or "Sobolev" it's all over
But eg think of the Alexander horned sphere. Both connected components are homology balls (again by Alexander duality), but one of them is not actually a ball
So it might still be possible (actually is)
18:28
@Daminark that seems like a rather weak way to differentiate between math jokes
4
LOL
Amazing
Lmaooooo
I'm not even going to try to stay current.
4
This is getting out of hand
18:30
Well, @Balarka, it is integral to matters at hand.
Now there are two of them...?
And humor does tend to fall flat here.
(Maybe getting too technical now.)
LOL
Exactly, the level of technicality in both of the jokes is great
This is all 'cuz Demonark showed up.
Wait flat for me means flat modules, what's the analysis term?
18:32
Demonark may have started it, but we all played parts in integrating the jokes.
@Ted I have followed your advice for seasoning creamed mushrooms and it turned out great
you advised for tarragon + thyme over thyme + sage + rosemary
@Daminark Flat site over a topos
The word "module" is meaningless to me
Ricci curvature = 0?
He knows what flat means, he's just kidding (Also, that's Ricci-flat)
I think we've ended this class of puns, though.
18:34
I also tried an Asian twist with dried shiitake and Szechuan pepper
sounds fit
error 404, no more equivalence relations found
I had mushroom pasta with spinach and ricotta today
Good thing we've resolved that
it was vile
@Daminark doN't
18:35
Hi @AkivaWeinberger
I'm actually cracking up IRL @Igjo
yeah, if we leave even a little kernel of pun behind it's sure to reproduce itself
Shut up
18:36
@Mathein: Glad to be of service :P
Two weeks left in this country
if you leave a little cokernel of pun behind it's sure to me back
Demonark: There are integral and flat currents, among others.
Ah I haven't heard of a flat current before
Oh I just thought you meant flat in the geometry sense
18:37
Nope.
That thought came to mind but it also felt like a bit of a stretch
I was on a current roll. Maybe even black current roll.
@TedShifrin oh and for mother's day I made tagliatelle, salmon steaks, leaf spinach and white wine butter sauce
You can't keep making puns which only geometric measure theorists would get!
Very old school, @Mathein.
18:38
I think at this point we're getting into the realm of food puns
By the way, I've decided:
@Balarka: It's my revenge against all the topos/scheme s**t here.
which I find a bit indigestible
instead of studying Hebrew or Spanish in college (my two second languages that I'm definitely not fluent in)
I'm gonna try to learn Japanese instead
Japanese calling it
Darn sniped
18:39
LOL
DogAteMy: In all seriousness, for grad school, you should learn some of French, German, or Russian. Most top departments still require one of those (two in my day).
'cause I think I'll gain more from being able to understand and speak four languages somewhat, than understand and speak three languages well
@Ted are foreign languages required in American departments?
Yes, although computer skills have replaced the second language most places.
18:40
Russian's good if you're in a rush
sorry for the romaji but: nihongo-no benkyo-wa tanoshi desu
@TedShifrin in terms of topos s***, the example which always makes me roll my eyes is the first page of the paper here: encyclospace.org/special/answer_to_tymoczko.pdf
you kana't be doing this rn
As in, required to learn them in grad school, or required to know them to apply? Confused
@Daminark USSR theme plays
18:41
@MatheinBoulomenos "Studying Japanese is fun"?
One has to prove technical reading knowledge/translation test.
In grad school, some have requirements that you translate some piece of math from said language into English
@MatheinBoulomenos tanoshii?
@LeakyNun oh right
18:41
Madison interestingly enough doesn't have a requirement of that sort
"We can say the same about Tymoczko’s worries concerning the sophistication
of some mathematical approaches used by Mazzola to delve into the intricacies
of musical phenomena. From his examination of Mazzola’s The Topos of Music,
he concludes [11] that Mazzola is tacitly asserting “If you cannot learn algebraic
geometry [...], then you have no business trying to understand Mozart”. Such
a phrase is similar to “If you cannot learn probability and statistics, then you
have no business trying to count the population of a city”. Of course you
I proved German by showing 4 semesters of college study. And then I took the French test (since obviously my French was/is way better than my German).
comparing the usage of algebraic geometry in music theory to the usage of prob/stats in the usage of population counting
@Ted the scholarship app required that I have a formal German language certificate
18:42
I'm taking an intro Japanese course next term and I'm planning to troll it by talking old-fashioned/over the top like a samurai or an anime character
is about as silly an analogy as I could ever hope to come up with
@ÍgjøgnumMeg, for studying in Germany that isn't so far-fetched.
@Ted yeah that makes sense, but universities in the Netherlands don't require any Dutch language (as far as I know)
Demonark: I hope you've looked up the definitions of integral and flat currents by now.
With a dictionary? @TedShifrin
18:43
idk
Yes, DogAteMy.
@ÍgjøgnumMeg there are far more English language courses in the Netherlands than in Germany
@Mathein kore wa ...
I think I could probably do French using a dictionary and my knowledge of Spanish… and math papers are mostly equations anyway?
waga na-wa Mathein de aru
18:44
NANI
I dunno, this is the first I'm hearing about this
Though I suspect it'll probably be useful to me to learn mathematical French. I spoke some in the past so I can probably still handle the grammar, mostly just need a glossary of some math words (e.g. manifold = variete + accents)
I'm kinda worried
@Balarka hahaha
Just translate Federer
18:44
I've read math in Spanish
@Daminark ezpz
A professor of mine had a friend who actually did that in grad school
I've read some Bourbaki actually
And the examiner was like, dang I can't find enough words
Borebaki
18:45
the French is managable with Latin and Italian knowledge
There's no significant publication of math in Spanish, DogAteMy. Nor in Hebrew.
@Mathein are there Russian language courses in Heidelberg? :D
@ÍgjøgnumMeg yes.
is learning science essential in mother tongue?
18:46
there are a lot of languages offered
@Mathein sounds great, might actually take one of those
When they test you, do you get to choose what subject the paper is in?
@SubhasisBiswas I don't think so
I should definitely learn French (easier) and Russian (not in the near future) at some point
Gromov still has untranslated papers in Russian
And like are you translating an entire paper or just a page
18:47
yes but
Learning the vocabulary to read a math paper in another language is generally easy.
if you translate from Russian to English, you still have to figure out how to translate from Gromow to Russian
I wouldn't say it is alike to actually learning (part of) the language though. Unfortunately. :(
@Semiclassical Yes, that's usually the hardest part
Not usually, DogAteMy. They can just choose the paper and hand it to you.
Usually 5 pages or so.
18:48
Wow, OK
I was reading his "Partial Differential Relations" a few days ago. He does completely absurd things
The French exam I took Mo Hirsch chose some writings of Thom, so it was tons of words and almost no symbols.
@TedShifrin do you enjoy refereeing papers?
To prove h-principles he introduces quasi-topological spaces which are like, sets with a specified class of maps from topological spaces which he calls the collection of continuous functions. This is like an etale topology.
And then he looks at sheaves on manifolds with values in quasi-topological spaces
Not particularly, @anakhro. There are a lot of horribly written papers out there. I didn't get my share of great papers to referee, which is OK.
18:49
In modern terminologies it's like a simplicial sheaf on an etale site
He's crazy to have developed all this by himself
@TedShifrin heh. Did you ever have the rare paper you refereed that you really enjoyed?
I remember being sent a paper of Lawson to referee, and that would have been great, but I was too busy with stuff and had to decline.
Okay actually now that this has come up, so I know when you're in academia you're writing papers, teaching, advising grad students, applying to grants, and apparently refereeing papers, what else is involved exactly?
OK so I still think I'm gonna take Japanese classes in college but I also think I'm gonna see how much French vocab I need to read some math
because I don't think I need an entire French course for that
Every French word is some collection of accents applied to the word "baguette"
18:52
lol
@anakhro: I've also refereed a number of textbooks for publishers. I just finished doing one I was decidedly unenthusiastic about. Now I mostly just decline everything because I'm a bum.
@TedShifrin what are the textbooks on typically?
@AkivaWeinberger in
dans ma chambre j'ai un hotel et un chat
18:54
Usually they're written on some form of paper-like substance @anakhro
je m'appelle Claude
@Daminark sassy lil fellow
Now we know the namesake, demonark.
Dami on a roll today
@Daminark You're missing the HoTT book
That's a textbook but not written on a paper-like substance
Is this the first time you've seen me pull such a stunt? I'm surprised
Ya got me @Balarka
I think this would be an exquisite time for me to take a lunch break.
18:56
looks up what HoTT is written on
HoTT is published, though
You can get paper copies from them
Alright now that Ted's heading out let's talk about differential geometry
I thought it's more of a philosophy thing to write on substance
Lol
@MatheinBoulomenos Clearly Voevodsky used to do cocaine
How else can you come up with univalent foundations

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