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10:00 PM
but couldn't.
So I tried googling it, and now I give up.
 
@Balarka: When you've learned what a Leray cover is, explicitly compute $H^i(\Bbb P^1,\mathscr O)$ and $H^i(\Bbb P^1,\Omega)$ for $i=0,1$.
You don't mean John Nash, do you, Nate?
 
@TedShifrin Okay, thanks.
I'll bookmark those
 
I've forgotten if Forster explicitly does those or gives them as exercises.
I could even tell you to do $\Bbb P^2$ :P
 
not rendering for me.
oh there we go
bad connection me guesses
@TedShifrin are you seeing somebody/ married / dating somebody.
Very personal question, but I've always wondered.
 
LOL ... I've announced various times that I'm gay. Dating occasionally.
 
10:08 PM
I know that you're gay, of course.
I didn't ask that :)
 
One of the reasons I moved across the country was to improve the social situation. We'll see ...
 
I will also announce that many people think I am gay, but I am actually not gay.
 
No, Jasper, you just comment to an unordinary extent about the looks of men.
 
LOL
 
Well, I don't know enough about America's stance on gay marriage or gay rights, but I will say that I truly hope that it does improve without knowing how bad it was where you lived before.
 
10:09 PM
To quote Seinfeld, "not that there's anything wrong with that."
America is going downhill quickly, Nate, with hate and weapons ruling the day.
But back to math.
 
Shit, move to Canada.
 
Did Russia sell Alaska to America long ago?
I think I read that somewhere...
 
LOL ... Sarah Palin can see Russia from her kitchen window.
 
did they sell it?
or just give it up
 
I don't remember the history.
 
10:12 PM
I don't mean to ask you personal questions that make you feel uncomfortable, Ted.
 
I don't feel uncomfortable, but I'm sure someone will come and get us flagged for inappropriate conversation :)
 
You can ask me anything, but there are some things I cannot reveal in this chat.
 
:(
 
ze obsessive flagger is still out there somewhere
 
But if you email me I will say more, lol.
@BalarkaSen What got flagged now?
 
10:13 PM
I still have my suspicions, Balarka, tantrums notwithstanding.
 
They should just remove the flag feature.
 
No, if there's truly offensive discussion, or personal attacks, it's necessary.
 
@Ted They seem to be really triggered by being called a normie though
 
I thought there is no more normie discussion in this room?
 
Seems stooopid to me.
 
10:15 PM
we need active mods.
 
Probably the best idea is to have a flag feature but abuse of it comes with a penalty
 
No, we need adult participants in the room, not petulant children.
 
@ted :(
 
And many of the teenagers in here behave better than the adults.
 
most baby boomers hate us @TedShifrin
 
10:16 PM
@Ted :)
 
The change of face @Balarka
 
I think DogAteMy has been a contributing adult as long as he's been here.
 
@Daminark I'm secretly flowey
 
Anyways @TedShifrin I was asking about your partner due to wanting to know who'd you bring if you did ever visit me and the gf.
 
10:17 PM
LOL, Nate ... I think you have more important things to spend time on :P
 
Nah
I have no friends to begin with :)
 
Maybe I will visit you too in future @Dodsy, lol.
 
well, work on that
 
I tried to.
 
@Dodsy Well, it's good that you have your girlfriend, lol.
 
10:19 PM
Exactly!
she's my best friend!
 
I have not dated in my entire life, lol.
 
@Jasper ofc you can visit, mein freund.
I've never had a friend in my entire life.
oh sorry, I did
 
@Dodsy Really? Hmm
 
@BalarkaSen I'm actually proud of my being Sans
 
he died in a car crash
 
10:20 PM
@Dodsy That's sad.
 
yeah my sister came into my room and said "eric died" and I said "okay please get out of my room" and she said "no nate, eric died" then I started bawling.
I think that was the most real moment I've ever had with my sister.
 
I imagine you are tall and thin for some reason. Am I right @Dodsy?
 
HAH no.
I imagine you short and stocky. Is that right?
 
Well, I am average all around.
 
I am 5'11.
 
10:24 PM
Same @Dodsy
 
@Daminark :o
 
@Daminark Now my head's playing Sans theme on the background.
 
I think I got that image because of the actor in the apes movie you used as your pic @Dodsy
 
lmfao
 
You can only lmao once, because after that, you have no more ass left.
 
10:25 PM
So there's this one kid in my math class who wears a suit to class everyday
O_O
 
nah, ass regenerates over time
6
 
I come to class in pajamas most of the time
 
@Semiclassical WTF
 
pajamas are good
 
10:27 PM
there really doesnt seem to be an end to asses in the world
you're always out of bubblegums, never out of asses
2
 
Solid reference
 
@Semiclassical We need a reference for that theorem, lol.
 
@TedShifrin, why did you choose to study math? If you want to answer : )
 
Balarka always says reddit comments here
 
Reddit does have some good answers.
 
10:30 PM
i am the very model of r/nocontext
(you do realize that's a good r/nocontext post, right? right??)
 
@Andreas: I liked it from a young age, and particularly got hooked on proofs and multivariable calculus early in college. I also found out my last year of high school that I could teach better than most of the teachers — and I loved that.
 
Hmm... ok
 
@AndreasAlmgren I asked a similar question.
if us and ted were born at the same time, ted would've discovered his love for math 10 years before us :P (more than 10 in my case)
 
I read a bunch of books when I was quite young that introduced me to interesting math ideas.
I now recommend reading anything Ian Stewart writes for non-experts. He's fantastic.
 
@TedShifrin James Stewart?
:P
 
10:35 PM
Um, no.
 
I feel like Canadian institutions only use james stewart because he's Canadian.
 
He's used all over America, too.
 
What a joke!
 
Well, there are worse books.
 
Ian Stewart has a Galois book, right?
 
10:37 PM
that's comforting.
 
Yes, Demonark. But I was talking about his more expository books for "lay persons."
 
@TedShifrin he was handsome in his young age
 
He's also got a complex analysis which I was fond of (and which i still continue to kick myself for losing track of)
 
He was quite a musician and supporter of the arts. He built a concert hall home.
He also happened to be gay. Not that it matters ...
 
@Dodsy, I'm 18 so I don't know if the 10 years would have been true in my case. You may not have meant it that way, though :D. @TedShifrin Dark secrets revealed... any particular book of Ian Stewart that you would recommend?
 
10:40 PM
@AndreasAlmgren then that 10 years does apply to you.
Ted was in the womb when he first read a first course on calculus.
 
Shaddup, Nate.
 
;P
 
I gave all those books away when I moved, Andreas. Let me google.
 
His mommy was dating a geek which was a course in itself.
 
My dad was a composer, actually.
 
10:44 PM
That's an interesting profession, Ted. Must've been an interesting childhood.
 
I grew up with a father who measured his worth based on how much money he made (though I would never discount his worth or how much he has accomplished)
 
Finally done with chemistry... we're still not talking much math I see
 
Well, if I start reading again maybe it will jumpstart it!
however, I am out of beer :S
 
Feel free
@Dodsy, did he apply these principles on you?
 
10:47 PM
I saw my father go from making ~30k a year
to making 250k a year.
 
imma start reading some math while listening to black metal shit
 
well more with obonuses.
@BalarkaSen nice
 
I suppose that put strains on the family
 
@BalarkaSen once I'm less occupied and can actually be at my computer for a bit we can do some Forster
 
It was an interesting upbringing.
But I am very proud of him because he accomplished his dreams.
 
10:49 PM
@Daminark Cool, that'd be nice.
 
Hmm... appears that I am totally wrong with what I think
 
About what?
hopefully something math related.
 
Your fathers upbringing of you, so not something very mathy xD
 
oh I see.
 
Actually I can do some right now
 
10:52 PM
Yee
 
Life is kind of like a genie that is out to make sure your life is miserable
 
Okay so just to be sure I got the preliminaries down
 
Wish to be smart and you get no recognition.
 
Rouche says that if $|f| < |g|$, then g and f+g have the same number of zeroes, yeah?
 
@Daminark Well, given a simple closed curve $\gamma$ on that plane and hol functions $f, g$ containing that curve, if $|f| < |g|$ along that curve, then $g$ and $f + g$ have the same number of zeroes inside the curve, yea
 
10:56 PM
Actually there's apparently a stronger version
If |f-g| < |f| + |g|
 
Assuming $f$ and $g$ doesn't have zeroes directly on the curve
@Daminark Oh yeah I see. Hm.
 
Yeah
So you can prove that via argument principle
 
Basically we want $\{f + tg\}_{t \in [0, 1]}$ to be a homotopy of holomorphic functions not vanishing on $\gamma$
If $f + tg = 0$ happened for some point on $\gamma$, then there $f = -tg$
Aka $|f| = t|g|$
 
And you can prove argument principle via residue
Yeah that makes sense
 
@Daminark Ah, hypothesis was $|f| > |g|$, not $|f| < |g|$
 
10:58 PM
Okay so rolling with Rouche
 
Which would contradict $|f| = t|g| < |g|$
But yeah otherwise look at $\{tf + g\}$
doesn't matter
 
You wanna get open mapping theorem
So let's say U is open, f is holomorphic on U
 
(Actually Forster proves open mapping theorem, as well as all the relevant theorems beyond the very basics of complex analysis, in Ch 1. Doesn't require Rouch\'e)
@Daminark Right
 
Oh does it?
 
Yup
 
11:01 PM
Okay lol, I was using open mapping to get inverse function theorem
 
:o
 
But alright I'll jump into Forster directly then
 
He proves a big theorem on the local description of holomorphic maps between Riemann surfaces that does it all
@Daminark You don't actually need open mapping to get inverse function theorem. It's kinda trivial once you know the inverse function theorem for smooth functions :)
 
well I'm off. Bye @AndreasAlmgren @TedShifrin @Daminark @BalarkaSen @Semiclassical
 
Cya
 
11:02 PM
Okay so Riemann surface is connected 2-manifold with charts whose compatibility is biholomorphic
 
Wait didn't you see that the smooth function version is a bad one to use?
See you @Dodsy!
 
I meant trying to do that same Banach fixed pt proof is bad
 
Oh lol
 
But you can directly use it
 
11:03 PM
True
Okay so we know the holomorphic function has an inverse which is real smooth
We need to get C-R
 
Exactly. Actually, you need to check that $f'(z_0) \neq 0$ also means Jacobian of $f$ is nondegenerate but that should be easy to check
 
Oh isn't it just like
 
where $f : \Bbb C \to \Bbb C$
 
The inverse matrix of a rotation dilation is still a rotation dilation?
Like that's obviously true
 
Yeah bam that's it
 
11:06 PM
bye @Dodsy
 
That was quick :P
 
Dank, I'm satisfied
 
Onto Forster
 
Okay so now I wanna prove what it said about P1 being homeomorphic to S^2
 
Hello
I have a question
 
11:08 PM
And also I wanna show that's the same as CP^1
 
it's a short exercise
Did you see that if $f$ is a meromorphic function on a Riemann surface $X$ you can extend it to a holomorphic map $f : X \to \Bbb P^1$?
unsure which pace you're powering through thus asking
 
Suppose that we have that $\alpha^{\frac{N-1}{p_1}}, \dots, \alpha^{\frac{N-1}{p_k}} \neq 1$ where $p_1, \dots, p_k$ the prime divisors of $N-1$. Then can we deduce that $N$ is a prime or not? And if for some $p_i$ it holds that $\alpha^{\frac{N-1}{p_i}}=1$ do we deduce that $N$ is composite? If so, why?
 
I mean I have only seen the definition of a Riemann surface and of a meromorphic function
 
ok ok
 
Actually I dunno much about meromorphic functions
Will that also be contained in Forster?
Or should I read something else?
 
11:14 PM
Forster defines it in Ch 1 section 1
Aren't you reading it
 
I mean I'm stopping to do the P1 exercise
 
Ah ok
For sure
 
Oh isn't that just gonna be stereographic projection?
Like just the homeomorphism
 
Right.
 
And then infinity is the North Pole
 
11:16 PM
Notice that the topology on $\Bbb P^1 = \Bbb C \cup \{\infty\}$ is just the usual topology on $\Bbb C$ plus complement of compact subsets of $\Bbb C$ for neighborhoods of $\infty$.
@Daminark Yeah.
 
Hi @BalarkaSen
Did you see my question?
 
I did but I am not going to think about it.
Maybe someone else can help
 
Is CP^1 homeomorphic to Gr(2,4)?
And by homeomorphic I mean basically the exact same
 
Ah, good question, no.
Not all 2-subspaces of R^4 = C^2 are actually complex subspaces.
 
Wait really?
Ah
That makes sense
 
11:22 PM
So CP^1 is obviously a submanifold of Gr(2,4), I think. Well, maybe make that oriented Grassmannian.
Not sure if I can extract much more out of that.
Which is interesting because the oriented Gr(2,4) is homeomorphic to S^2xS^2
Make that S^2=CP^1 sits as a "torus knot surface" in that
Ted would know this picture
 
Okay so we can embed C^n into CP^n by choosing one of the spaces, right?
 
Sorry, what do you mean by choosing one of the spaces?
 
I mean CP^n is a bunch of hyperplanes
Pick one of them
 
Er, every point of CP^n corresponds to a 1-dimensional subspace in C^(n+1)
How do you "pick" them?
And how does the produce an embedding of C^n into CP^n?
 
Oh whoops, nevermind
Brain fart
 
11:29 PM
Here's a hint. Do you know a coordinate representation for every point in CP^n?
There's a convenient way to write this.
 
I don't know any coordinates in CPn
 
Ok, let me explain
Say you pick a point in $\Bbb{CP}^n$. That corresponds to a copy of $\Bbb C \subset \Bbb C^{n+1}$
Choose a vector in that copy of $\Bbb C$.
That can be written as $(z_0, z_1, \cdots, z_n)$ for $z_i$ complex numbers.
But if I multiply them by $\lambda$ to get $(\lambda z_0, \lambda z_1, \cdots, \lambda z_n)$ for $\lambda \neq 0$ that also corresponds to a vector in that specific copy of $\Bbb C$.
So you set up a "homogenenous coordinates" for $\Bbb{CP}^n$, where every point can be written as $[z_0 : z_1 : \cdots : z_n]$, $z_i$ complex numbers, and in this coordinates $[\lambda z_0 : \cdots : \lambda z_n] = [z_0 : \cdots : z_n]$ for $\lambda \neq 0$.
 
Okay imma try to avoid coordinates
 
It's going to get harder to understand without coordinates.
(The whole point is that this gives CP^n a complex manifold structure)
I mean you can do it but it's harder to understand
The whole shit is similar to how $\Bbb{RP}^1 \cong S^1$, if you remember that.
 
11:46 PM
Alright at some point in time I'll figure out how to avoid them but for now I'll just roll with it
 
Yeah so notice that $z_0 \neq 0$ gives you an embedding of $\Bbb C^n$ in $\Bbb{CP}^n$
 
Hmm
 
'Cuz if $z_0 \neq 0$ multiply by $1/z_0$
You have all the points of the form $[1 : z_1/z_0 : \cdots : z_n/z_0]$
The $n$ coordinates $z_i/z_0$ parametrize a chart $\Bbb C^n$ in $\Bbb{CP}^n$
 
Okay so given two homeomorphic topological manifolds, we can pass a complex structure on one to the other, right?
Just by composing with that homeomorphism/inverse
 
Yeah
 
11:57 PM
Okay so, is the product of complex manifolds a manifold?
 
Yep
You mean "[...] product of complex manifolds a complex manifold", but yeah
 
Actually I didn't need that last part
Is it somewhat easier to prove that $S^1\times S^1$ is a Riemann surface?
 
Oh yeah example 1 or something in Forster
 

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