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14:00
Seriously?
@Venus Yeap.
I can only see it is done by using substitution $u=\tan x$
@Venus you mean you only use that substitution and you're done? I didn't use that.
@BalarkaSen In fact $G/Z(G)$ cannot be cyclic unless it is trivial.
@BalarkaSen What about the $[G,G]$ part?
What is [G, G] again :P The subgroup of G \times G consisting of conjugate elements?
14:05
@BalarkaSen The commutator subgroup.
@Chris'ssis That's how I'll do it, but not sure it works
@Venus OK
I forgot what it is. Is that the subgroup of G generated by [a, b]s?
@Venus I can also do it for $$\int_0^1 \arctan(x) \log^{2015}(x) \ dx$$
@BalarkaSen This is basic stuff. You said it.
14:07
What??
@Venus Seriously.
@PedroTamaroff I didn't note that [G, G] part.
Anyway, I googled.
It is the subgroup generated by all the commutators.
Ya I know @Chris'ssis. You're not kidding. I'm just shocked
@Venus I know to do it for all positive integers powers.
Looking the previously closed-form, it seems the formula for general form $$\int_0^1\arctan(x)\ln^k(x)\,dx=\sum_{n=0}^k\cdots$$
14:11
@Venus I've never ever seen such a formula before. I know what to do, but I didn't put all in a general form yet.
Just my guess
A random guess
@PedroTamaroff $G$ is not abelian. Thus $[G, G]$ is nontrivial.
And $[G, G] \leq G$. So it's either of order $p$, $p^2$ or $p^3$.
Hmm. $G/[G, G]$ is abelian.
@BalarkaSen $G/[G,G]$ has a universal property, so to speak.
Put in other words, it is the smallest normal subgroup of $G$ such that $G/N$ is abelian.
Being that [G, G] is the largest normal subgroup of G such that quotienting out gives abelian?
Jinx.
Not largest. Smallest.
14:16
I vaguely remember the word "abelianization"
$G/[G,G]$ is the largest abelian quotient of $G$.
Yeah.
$G/[G, G] \leq Z(G)$
@Venus I only nicely ask you not to post my questions on main. I don't wanna share all things on main. :D
So it's of order $p$. Hence $[G, G]$ is of order $p^2$.
Wait, what.
Your problem statement is garbled up @PedroTamaroff
No it is not.
14:20
You meant $G/Z(G) = G/[G, G] = C_p^2$ instead of what your wrote.
I think.
I meant $G/Z(G)=C_p^2$ and $Z(G)=[G,G]$.
@Ashwin You never put it up
Aha.
$[G, G] \leq Z(G)$ is clear. And $|Z(G)| = p$. So we only have to show that $[G, G]$ is not trivial but that is true as $G$ is not abelian.
So $[G, G]$ is of order $p$ and is all of $Z(G)$
Congratulations.
@BalarkaSen Suppose $H\lhd G$ and $H\cap [G,G]=1$. Then $H\leqslant Z(G)$.
Here $G$ is arbitrary.
@Chris'ssis OK, I won't. You have my words
It seems I have a trouble with my internet connection
14:25
Hi @Robjohn
OK, Gotta go now. Bye
@Venus See ya.
One thing that is good about the girlfriend being gone is that I can sleep whenever, but there are a thousand things bad about it, sleeping whenever is also one of those :\
@Chris'ssis Wish me luck for my exams :-)
@PedroTamaroff Normality implies $G/H$ makes sense.
14:26
@PedroTamaroff Not exactly. I mistakenly assumed the field extended the given ring.
@KarlKronenfeld Ah. OK.
Hmm. And $G/H \cap G/[G, G]$ is empty.
@Karl what is le problem?
@Venus I wish you had much luck! The luck I myself need at the job interviews. :-)
@KarlKronenfeld Did you like the exposition, or did you find it too simple? It strikes to me as simple, maybe because the definitions are so well made.
@PedroTamaroff there is something I think would be really cool to look into, once I've played around with it a bit, I'll email it to you.
Huy
Huy
14:29
@Committingtoachallenge: How come you couldn't sleep whenever, before?
@PedroTamaroff It is not simplistic, imo.
@Huy She sleeps at a normal time, so it would be rude for me to keep her up by sleeping at erratic times
@KarlKronenfeld Ah. What about the style?
Huy
Huy
@Committingtoachallenge: Why would you keep her up by sleeping at erratic times?
@Huy Our house isn't very large, light and sound would cause problems
Huy
Huy
14:31
@Committingtoachallenge: Many problems sum up.
@Huy What do you mean?
Huy
Huy
@Committingtoachallenge: It doesn't matter.
Hi!!! Could someone help me at this exercise?

http://math.stackexchange.com/questions/1006120/at-which-p-adic-fields-does-the-equation-have-no-solution
@BalarkaSen Did you solve it?
@Huy You have a thing against relationships don't you?
14:32
@PedroTamaroff eating. i think i can do it though.
@Huy Or was that just in regards to the age of UserX
Huy
Huy
@Committingtoachallenge: I think that would be problematic to my girlfriend.
@BalarkaSen Cannot you chew and think at the same time? ;D
Huy
Huy
@Committingtoachallenge: You must be confusing me with somebody else.
@Huy Oh I am apologies, it was Alec Teal
14:33
The main thing is that the statement of the big theorem in the first section is not motivated well enough. That said, I am unsure exactly how to improve it atm. @PedroTamaroff
Huy
Huy
Don't worry, nothing to apologise for, @Committingtoachallenge.
$\frac11>\ln\frac21>\frac12>\ln\frac32>\frac13>\ln\frac43>\frac14>\ln\frac54> \dotsb$
@KarlKronenfeld Yes, I was told that by my prof. She was a bit more satisfied when we noted Artinian rings are Hilbert(ian)?
@PedroTamaroff Ian Hilbert?
I should mention that that (the thing I posted above) is only true for the natural logarithm (base $e$), and not for a logarithm to any other base.
14:36
@BalarkaSen No. Noether-ian, Artin-ian, Hilbert-ian.
I was trying to make a pun.
Using that (the thing I posted above), and without using any calculus, you can prove that $1-\frac12+\frac13-\frac14+\dotsb=\ln2$. I won't post a proof here.
I. Hilbert sounds like the author of the fraud papers generated by the automated mathematical paper generator site. I. Hilbert, S. Newton, X. Galileo...
OK back to the problem.
Ah, I think I have it.
Is $f(t) = \log(\frac{t-a}{t-b})$ locally integrable?
@ROBJOHN
$H \lhd G$ and $[G, G]$ is a subgroup of $G$. Then $[G, G] \cdot H/H \cong [G, G]/(H \cap [G, G]) \cong [G, G]$
Hrm, no, I don't think that's it.
14:50
@Huy I need help again. Can you see what manga are released in mangafox? Thanks
Huy
Huy
@Anastasiya-Romanova: Sure, what exactly do you need?
@Huy Bleach, Detective Conan, HxH, Bloody Monday
@RajeshD yes
Huy
Huy
@Anastasiya-Romanova: Bleach goes up to chapter 608, if I'm not mistaken, on mangafox.
@Anastasiya-Romanova: That chapter was released just two days ago. Do you mean that?
@RajeshD as long as you allow logs of negative numbers
14:53
@Huy Yeah. Are they still fighting?
Huy
Huy
@Anastasiya-Romanova: I don't know, I never read Bleach, sorry.
@BalarkaSen Pick an element of $H$. Show it commutes with every element of $G$.
That's what you have to do.
@Huy How about Conan?
Huy
Huy
@Anastasiya-Romanova: 911, released on 22 Nov.
@Huy Are you serious?
14:55
Hint Pick $g\in G$; $h\in H$. Then $ghg^{-1}h^{-1}$ is a commutator, and it is in $H$ because $ghg^{-1}\in H$ by normality.
Huy
Huy
@Anastasiya-Romanova: Yes. Why?
Take $h \in H$. $g \in G$ be some arbitrary elt. $hgh^{-1}g^{-1}$ is in $[G, G]$.
Jinx again
Yes, Balarka.
The last release is 22 Nov?
Huy
Huy
@Anastasiya-Romanova: That's what it says on the website.
14:56
Then $ghg^{-1}h^{-1}\in H\cap G'=1$.
@Huy Ho about HxH?
Yes, yes, I was doing it.
Huy
Huy
@Anastasiya-Romanova: Still no new release.
To "avoid" this calculation, note that you want to see that $[G,H]$ is trivial.
That's a cool trick.
14:57
Normality means precisely that $[G,H]\lhd H$.
@Alizter In case you haven't known yet. Do take part in this contest. @Integrator too. Ask Ruben too. Thanks.
And hence $[G,H]\cap [G,G]=[G,H]\leqslant H\cap [G,G]=1$.
@Huy OK thanks... :(
Huy
Huy
@Anastasiya-Romanova: Do you want any of them?
14:58
@Huy Do you know why it hasn't released yet?
@PedroTamaroff Another problem!
Huy
Huy
@Anastasiya-Romanova: I don't. If it has been released in original language, it might be that translation takes up a bit of time (I assume mangas on mangafox are in English).
What can we say about $$\sum_{n=1}^{\infty} \frac{H_{4n-3}}{(4n-3)^2}$$?
@Huy The last chapter I read was chapter 349
@BalarkaSen Suppose $G$ is a $p$-group. Then $\Phi(G)=G^p[G,G]$.
Huy
Huy
14:59
@Anastasiya-Romanova: It is the latest on mangafox, for HxH.
@PedroTamaroff what in the name of typhoons is $\Phi(G)$?
@robjohn have you ever seen the series I just posted above?
That's the Frattini subgroup of $G$.
I forgot what it is.
@Huy How about Bloody Monday?
15:00
I think you told me about it.
Huy
Huy
@Anastasiya-Romanova: Bloody Monday 1 or 2? I see two different ones.
@Anastasiya-Romanova: I even see a "Bloody Monday - Last Season".
Season 3
Yup, the last season
Yes, probably. Nevermind. Consider this problem. Suppose that $H$ is normal in $G$, and let $P$ be a Sylow subgroup of $H$. Then $G=H N_G(P)$.
Huy
Huy
@Anastasiya-Romanova: 36, released on 4 Nov.
Bah!
What are they doing over there
Huy
Huy
15:02
@Anastasiya-Romanova: I'm afraid I don't know the answer to that question.
More generally, suppose that $G$ is a group that acts on a set $X$, and suppose that $H$ is a subgroup that acts transitively on $X$. Then $G=H {\rm stab}_G(x)$ for any $x\in X$.
OK, lets see.
Thanks anyway for your help @Huy. Bye. Cya.
Huy
Huy
@Anastasiya-Romanova: No problem. Have a good night.
15:03
In the above, $G$ acts by conjugation on the set of Sylow subgroups of $H$, since $H$ is normal.
Okay @Huy, you too. Happy Sunday
right i think i have done that before. you probably gave me the problem. let's see if i can reconstruct the solution.
@PedroTamaroff @robjohn @DanielFischer @MikeMiller @BalarkaSen

$$f(x,y)=-4x^2y^2+(x^2+y^2)^3$$
$$g(x,y)=-y^3+3x^2y+(x^2+y^2)^2$$

$$P=(0,0)$$


$$f(x,y)=-4x^2y^2+(x^2+y^2)^3</math>: <math>f_4(x,y)=-4x^2y^2 \Rightarrow m_P(f)=4$$

$$g(x,y)=-y^3+3x^2y+(x^2+y^2)^2: g_3(x,y)=-y^3+3x^2y \Rightarrow m_P(g)=3$$

The tangents in $P=(0,0)$
of $f$ are $x=0$ and $y=0$
of $g$ are $y(3x^2-y^2)=0 \Rightarrow y=0, \sqrt{3}x+y=0, \sqrt{3}x-y=0$

So, $f$ and $g$ have a coomon tangent, $y=0$.

So, the intersection isn't tranversal.
@evinda STOP DOING THAT.
2
Aw hell
15:05
You always post some humongous thing.
the whole chat blew up
Post it on main.
@evinda
@PedroTamaroff I did but I didn't get an anwer and I wanted you to ask if you have an idea..
hi, off topic: Can someone help explain how the fact that $|f|^p$ is integrable over $E$ being used in the last line.
15:21
hmm... those of you who make your email addresses publicly available, have you ever gotten random math questions in the mail?
@Chris'ssis Do you have a closed form for the sum? I know we can do $2n-1$, but I would have to think harder about $4n-3$
@Mike how do you check if others can see your email address?
@teadawg1337 Unless you put it in your 'about me', they can't. I put mine in my 'about me'.
@robjohn Yeah, there must be a closed form.
@Chris'ssis but you don't have it yet?
15:27
@PedroTamaroff $H \cdot N_G(P)$ is $\{hg : hgPg^{-1}h^{-1} = P\}$. This means $gPg^{-1} = h^{-1}P h$. The latter is another Sylow $p$ subgroup of $H$. That means $gPg^{-1}$ is a Sylow $p$ subgroup of $H$. That means $gPg^{-1} \leq H$, implying $H$ is normal in $G$.
@Mike That's what I thought, just wanted to make sure
@robjohn Well, I have it in the following minutes ... (it's a matter of minutes)
LOL I reverse engineered.
Hi @Robjohn : Great to see you after a long time. I missed something. It is $\log|\frac{t-a}{t-b}|$
@RajeshD then that is definitely locally integrable.
15:30
@Robjohn : I am basically interested in this result. Let $f$ be a piecwise smooth function in $L^2$, then does the Hilbert transform $f_h$ is in $L^1$?
if not $L^1$, atleast locally integrable?
@BalarkaSen: Are you free for checking a field theory problem?
@BalarkaSen That's OK.
Now do things properly.
Pick $g\in G$. You want to write it has $hk$ where $h\in H$ and $kPk^{-1}=P$.
Now given $P$ and $gPg^{-1}$ are both $p$-Sylow subgroups of $H$ for some $p$, since $H$ is normal. This means that there is $h\in H$ such that...
@RajeshD I'd have to think about it, but I'd doubt it. I have to walk the dog, but I will think about it. One thing to think about is the fact that the Hilbert transform is essentially it's own inverse.
@robjohn Done
@M.N.C.E. have you ever seen before the series I posted above?
$$\sum_{n=1}^{\infty} \frac{H_{4n-3}}{(4n-3)^2}$$
@Robjohn : Valid point. So I guess I be happy with the "locally integrable" result.
15:43
@PedroTamaroff: A problem on fields? Cyclotomic extension?
@RajeshD Wait... The Hilbert transform is an isometry on $L^2$. Therefore, the Hilbert transform of an $L^2$ function is in $L^2$ and therefore, locally $L^1$.
@robjohn great!
:18945218 Ah... I often don't think of things involving $\mathrm{Li}_3$ to be closed forms, but I may expand my horizons :-)
@Integrator How do you do that ? :o
@robjohn :D
15:47
Off to the park... BBL
I am back.
16:03
@Chris'ssis I think I've seen similar sums on SE. I'll give it a try.
@M.N.C.E. No need to compute it entirely. I was just curious to know your starting idea.
@Chris'ssis I would sum up the residues of $\dfrac{\pi\cot(\pi z)\psi_0(-4z)}{(4z+1)^2}$
@M.N.C.E. OK. I was thinking you had in mind a real method. Thanks!
@Chris'ssis Unfortuanely I don't :/ ... I presume you have one?
@M.N.C.E. Yes. I'll show you when I put things on paper.
16:07
@M.N.C.E. What is $\psi_0$?
@PedroTamaroff It's the digamma function
ADG
ADG
Hey please help me , I answered a question and someone just copied it, he got 2 upvotes and the accepted answer and mine was just neglected, here
@Chris'ssis I would look forward to that then.
Ah. I usually don't see the subscript used. I suspected that, yes.
@Pedro I'm used to seeing $\psi(z)$ as opposed to ${\psi}_z$
16:11
@ADG: Two comments. First, putting up a scan of handwriting, as opposed to a beautifully LaTeXed answer, is frowned upon. Second, the time marks would indicate he/she didn't copy you. His answer clearly took something like 10+ minutes to type, and you two posted more or less simultaneously. This sort of thing has happened to me numerous times.
hi @Pedro @teadawg!
Hmm, my notation is probably way off... Hello @Ted!
@TedShifrin Hello-.
@Mike: I got my first such recently. And the person made no effort to say who he was or why he was contacting me. I ignored it. I get enough stuff to work on :)
@M.N.C.E. To be more specific, I won't use the residues, but I need to make use of the complex numbers.
@TedShifrin Your first what?
16:16
@Mike asked earlier about whether those of us with our emails here public get people emailing us.
I'm not the best person to answer that, @Pedro. But all this stuff relates to questions about vector bundles in algebraic/analytic geometry.
BTW, you're missing a comma. I thought there was another Ted :P
@Ted Yes, mine was from a James Tortelli, or something similar, asking me about an algebra problem. As I have no idea who he is and have my own algebra problems to do...
@TedShifrin Mariano told me that the ring of regular functions over an algebraic variety has the same dimension as the variety. But that this fails for analytic varieties. However, he said, it happens that $\mathcal O(D)$ has many properties of dimension one domains, and every open set $D\subseteq\Bbb C$ is one dimensional, so it almost holds. =)
In particular, it has the property I stated.
16:22
Fratelli. Same guy who emailed me.
It has infinite Krull dimension though.
I want to see if I can prove that.
Sounds more like combinatorial number theory to me, @Mike.
@TedShifrin Fratelli... Interesting...
IT's a reasonable Italian name, @teadawg :)
16:24
@teadawg1337 "Fratello" means brother in Italian.
"Frat" is a prefix related to "brother."
"Fraternity", "fraternal", &c.
@TedShifrin It's quite easy to solve given the right frame of mind. I have to assume he picked our names by coming to this chat, so I'll wait until he shows himself here to say anything.
ADG
ADG
@Ted but why is his same exactly, atleast I think the thing that happens to you also happens to me or otherwise I won't have reached 5K, even after same answers everyone's style is different
@ADG, seriously: You think the guy copied your stuff and typed it all in in THREE minutes? No way. Oh, and included a Geometer's Sketchpad graphic, too?
Oh, it's an Italian name?? I haven't met any Italians in my life, I apologize for my ignorance...
@ADG Don't worry about rep.
It's silly.
16:27
Well, @teadawg, just so you know. My name has Russian origin. I don't know where "teadawg" comes from, although the dawg spelling makes me suspect my university.
@MikeMiller Help me out here. Let $D$ be a region in $\Bbb C$, and let $T$ be discrete in $D$. Shouldn't it be clear that $T'=\partial T\subseteq \partial D$?
I don't know what $T'$ is.
The derived set.
I don't know what the derived set is.
Set of limit points of $T$.
16:29
Hello!! How can I have to show that, in $\mathbb{R}^d$ with Lebesgue measure, the $L^p$ spaces are not comparable ??
@ADG: I believe Balarka told me a few months ago that a very involved answer I wrote to a very unusual question (and which took me several days to solve) ended up copied on another site, without any credit to me. Sadly, people do these things. So, even if you're right, it's part of life.
How is $\partial T \subset \partial D$?
@Ted "teadawg" is just my username. My initials are TEA, my friends called me "T-Dawg" in middle school, and 1337 because I enjoy videogames. Hence the username "teadawg1337"
Give examples to show neither containment holds, @MaryStar.
I guess I'm used to Dawg as coming from only UGA, @teadawg. I guess there are comics or videos that use it, too. My ignorance :P
Dawg is common across the country, @Ted, though I suspect people stopped using it about a decade ago.
16:31
I figured only people from GA were so ignorant, @Mike :D
@TedShifrin Could you give me a hint how to find such examples?
@MikeMiller Take $B(0,1)$. Take a set of discrete points in $B$ converging to $1$, call it $T$.
Then $T'=1\subsetneq \partial B$.
Yes, that was the point I was making.
16:32
Think about exponents on $|x|^r$ for some of them, @MaryStar. This is a standard sort of thing you should figure out for yourself.
@MikeMiller I've been using this username for about 5 years, so that's probably accurate
Perhaps you wrote the original question down wrong, @PedroTamaroff?
@Integrator Oh Nono :) I think I figured it out :D YAY!
@Ted How should I check the answers I've gotten so far on the exams you've sent me?
What's the context?
16:39
Oh, I misread.
=D
Huh? No it doesn't. Discrete sets aren't necessarily closed... you just gave a counterexample.
ok
@MikeMiller Yes, yes. But what I'm saying is true is $T'\subset \partial D$, not the other way around.
Here $T'=\overline T-T$.
You just gave an example where that's not true.
@MikeMiller Where what is not true?
That $T' \subset \partial D$.
16:41
@TedShifrin So, do I have to find a $r$ such that $(|x|^r)^n$ is integrable but not $(|x|^r)^m$ for some $n, m$ ??
How so? $T'=\{1\}$ is a subset of $S^1=\partial B(0,1)$.
Oh, I misread your example. Now do the exact same thing but have it converge to 0.
Oh. I'm being sloppy.
Yes it is.
@M.N.C.E. a nicer example is $$\sum_{n=1}^{\infty} \frac{H_{4n-3}}{(4n-3)^3}$$ without residues.
16:43
@MikeMiller At any rate, neither inclusion holds, it seems.
Yeah.
So what's the context?
Take a region $D$ and take a function $\mathfrak d:D\to\Bbb Z$.
Out for some jogging ...
Call it a divisor if it vanishes everywhere but on a discrete set of $D$.
This set, the support, call it $T$.
16:49
Well, then the book says "If $T$ is a discrete set in $\Bbb C$, then the set $T':=\overline T-T$ of all the accumulation points of $T$ in $\Bbb C$ is closed in $\Bbb C$. The region $\Bbb C-T'$ is the largest subset in which $T$ is closed. Every positive divisor on $D$ with support $T$ can be viewed as a positive divisor on $\Bbb C-T'\supseteq D$ with the same support [positive means it takes nonnegative values]. Clearly $T'\supseteq \partial D$."
Note that you're demanding that $D$ contain $T$...
This is much different than the question you asked. Here it is clearly true...
In my example, $B(0,1)$ contains $T$.
And in the c/e we constructed together it also contains $T'$, which by definition above $D$ does not.
16:52
@MikeMiller No, no. In my example. let $T$ be a sequence in $B(0,1)$ converging to $1$. Then $T'=\{1\}$ is not in $B(0,1)$. But is it in its boundary.
Anonymous
@Committingtoachallenge I still got 4 more hours to go :D
So it holds that $T'\subseteq \partial D$.
Yes, necessarily.
Anonymous
@Committingtoachallenge I will be posting from today,for sure!
So I guess that last inclusion is written backwards.
16:53
Yes.
That was my point all along. =P
What a pointless discussion.
:18945770 For most examples, $T'$ is usually finite, but $\partial D$ is sometimes a curve, which is uncountably infinite.
@MikeMiller Yes.
@TheArtist What's the answer then?
We just lost half an hour of our lives.
When I was studying riemann surfaces there wasn't any of this silly point-set consideration. I wonder what Remmert needs it for.
16:54
@MikeMiller Typos, typos everywhere.
@MikeMiller Weierstrass products.

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