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1:00 PM
or is it...(-2 rep for not accepting an answer)
 
hi @don legit graduate :)
 
Have you done rudin's principles O MA?
 
@PedroTamaroff look math.stackexchange.com/a/1080231/66223 great answer, the COMMENTS get upvotes, but the answer doesn't!
 
@pedro is English your first language?
 
1:05 PM
@AlecTeal Well, that answer is not really something.
 
It's a good homework hint!
 
"Don't bother doing..."
"...just be like"
 
Nothing for it at all -.-
 
You have an upvote and a downvote.
 
Huy
@PedroTamaroff: Can you check my rep? Someone is clearly serial downvoting me since yesterday.
 
1:06 PM
@huy I wonder why...
 
@PedroTamaroff I do that to encourage corner-cutting, to take the lazy route! You don't need to show the formal definition of convergence when you know multiplying convergent sequences converge, and so does adding them
It's to demonstrate that, "don't bother doing it the long way, you already know stuff, use it!"
 
@Huy System has already reverted 4.
 
Also nooby first year analysis question GOT 4 UPVOTES
 
@AlecTeal I would change the wording.
 
Rewording it would have a marginal influence on the utility of the answer @PedroTamaroff
It's not an English essay.
 
1:09 PM
Presentation is something important, specially in mathematics.
 
It was done deliberately @PedroTamaroff
 
If you include things like "BAM, failure." or "just be like" people will tend to not upvote you.
 
When I was a tard I was overly-formal everywhere, and would rarely use theorems - I was DELIBERATELY (caps :P) being casual about it.
 
@Alec I wouldn't worry about hats or reputation
 
But rep is the reward, the worthless thing I crave that shows appreciation or agreement
Upvotes improve my confidence too!
 
Huy
1:11 PM
@AlecTeal: There is a huge difference between being "casual" and using "nice language" whilst explaining maths.
 
@huy what topics made you enjoy omplex analysis?
 
But we do it all the time!
 
Huy
@AlecTeal: Look at this answer for example, it is not overly casual but also not overly formal, and yet he uses a lot of words you wouldn't find in a normal maths textbook: math.stackexchange.com/a/37268/3787
 
"Don't bother with that integral, be all like "it's the integral of an odd function over a a range -x to +x, so it is 0"
 
@pedro can you see If huy is ignoring me using the function or just reading them and not responding? Also was English your first language or not ??
 
1:16 PM
Anyway @PedroTamaroff you should get into the habit of upvoting rather than waiting for the 5th edition of an answer, it improves confidence because it means "someone else has agreed with you"
It causes no harm, it wont "devalue" the worth of rep
 
If $f$ is continuous on $[a,b]$, $f(a) = f(b) = 0$ and $f(x) = f'(x) + f""(x)$, prove that $f(x) = 0 \forall x \in [a,b]$
 
I don't know if Pedro is mean or it is just the normal language barrier between native and not
 
@VibhavPant wut?
 
I tried everything I could (except solving the differential equation), but couldnt get anywhere. any idea?
 
Link to quetion
@PedroTamaroff math.stackexchange.com/a/1087487/66223 is this worthless to you? If it's a good hint I'll upvote!
 
1:18 PM
@AlecTeal Something that has been troubling me of lately
 
@VibhavPant link to the question please
 
@vibhav so we have both endpoints of the interval 0 and we are proving that the integral is $0$?
 
@beginner where did you see the integral?
 
@AlecTeal oh. I haven't posted the question yet
 
@AlecTeal "You should get into the habit of upvoting."
 
1:19 PM
The function is zero all the way along, hence the integral is 0?
 
@PedroTamaroff I do where I see things I think "yes that's helpul"
 
@beginner I need to prove that the function is zero all the way along
 
@VibhavPant mean value theorem
 
Yes meaning the $\int_a^b f(x) =0$ I don't really know any calculus so that isprobly wrong
 
@AlecTeal I do not find your answer helpful, Alec.
 
1:21 PM
@beginner but so does a function like (x-(a+b)/2)/(b-a)
 
Are you just mean or English not irst language@pedro
 
@PedroTamaroff grr you're annoying
 
@AlecTeal So, $\exists c \in (a,b) : f(c) = f''(c)$? I'm not able to infer anything useful from it :(
 
@VibhavPant post a question
Have you tried contradiction, suppose there were a non-zero function, (WLOG) assume the function goes up from 0 initially, then f` >0
 
@AlecTeal How many times have you upvoted?
 
1:23 PM
@PedroTamaroff I dunno, but I try to upvote where I see 1) right or useful information 2) someone trying
 
You can check this in the "votes" tab in your profile.
 
Especially with newer users!
It gives them confidence
 
@AlecTeal Trying is not enough, usually.
 
104 @PedroTamaroff
Yeah @PedroTamaroff if you're a git.
 
What's a git?
 
1:25 PM
A version control system named after something ;)
 
Hi, guys. A brief question please: what are the options of integrating this? $$\int dx^2$$
 
git is a version control system Linus named after his personality because it is apparently a thing in Finland
 
But seriously I'm not going to format answers TO SIMPLE ANALYSIS questions like I am writing a textbook, nor should you expect me. The information is correct, the answer is an answer, upvotes build my confidence, I really appreciate even the comment ones it means "I have improved"
@VibhavPant no, Linus named it based on his thoughts of Perforce after they wanted to charge for use.
 
@AlecTeal OK. I don't mean to be comparing shoe sizes here or anything, but you just told me "you should get into the habit of upvoting rather than waiting for the 5th edition of an answer" -- I have cast almost 14.000 upvotes so far.
 
@PedroTamaroff I don't think the absolute measurement is very useful here.
I mean 1/4 accidents are caused by drunk drivers right? That means 3/4 are sober people! Best drive drunk everyone!
Drunk drivers cause fewer accidents than the sober ones, but that's not the point
 
1:28 PM
@AlecTeal You somehow deduced my voting habits from something I told you -- well, you didn't. But, still. It is not nice to be around prejudging people, eh? =)
 
@AlecTeal Wikipedia says: "Torvalds has quipped about the name git, which is British English slang meaning "unpleasant person". Torvalds said: "I'm an egotistical bastard, and I name all my projects after myself. First 'Linux', now 'git'"
 
I don't think the time period of using the site is that different in Pedro defence alec
 
@VibhavPant I was there during development, so I'll edit that page later, everyone hated Perfroce
@PedroTamaroff I didn't say "YOU'RE THE ONLY ONE NOT UPVOTING" but you have one hell of a problem about doing it
"I don't like 5 words you used, so not a good answer"
I mostly see your name on votes to close.
 
@AlecTeal That's partially a reason.
But it's not the main reason.
 
wasnt git developed because everyone hated BitKeeper?
 
1:31 PM
@AlecTeal You didn't say that, I know.
I hope I didn't give the impression you did.
 
@VibhavPant is that the Perforce system? Basically a company let Linux use it's usually paid for distributed VCS, then they said "pay us" everyone was like "you ****s" of course you cannot name a VCS **** so they chose "git"
Use your imagination for the missing word
No offense @PedroTamaroff
[BURN]
 
Huy
@AlecTeal: If you don't want to format answers to "simple analysis questions" then you also shouldn't be complaining about people not upvoting your answers.
 
@Huy math.stackexchange.com/questions/1080226/… the language was chosen deliberately - I'm not going to write 5 pages listing every definition and every theorem used.
 
Huy
@AlecTeal: Nobody forces you to do anything.
 
@Huy okay?
@Huy math.stackexchange.com/a/834795/66223 worthy of upvote despite it's length!
 
1:35 PM
@alec I think they just don't want you to put in casual phrases, keep the language formal, but you don't need to quantify everythin
 
@beginner shush.
 
@AlecTeal There's not reason to expect a long answer is of better quality.
 
Huy
@AlecTeal: Look, I received 15 upvotes for a single sentence: math.stackexchange.com/questions/1086559/…
 
I would answer 150.000 characters "A", that doesn't make my answer better.
 
@Alec why shush me? That is what they are saying, just write formal English, and do the math the same
 
1:36 PM
@PedroTamaroff you need to stop treating this site like everyone is at your level, a lot of people are not and are learning, and one nice encouraging thing from someone with high rep, or getting rep itself vastly boosts confidence and gives a sense of achievement. No one can deny this.
So stop being a [Git's working title] and use upvotes for encouragement not "Well I'm not upvoting that, I'd never publish that in a book on the subject" or whatever test it is that you use.
This applies to all of you BTW - this site is so unforgiving to new / learning people.
 
@AlecTeal If I praise incorrect answers, or poor answers, I would be doing more harm than good, Alec.
 
@PedroTamaroff don't praise incorrect ones, and don't pretend you think I was legitimately saying you should.
 
I was trying to help you improve your answer, and you reacted in a way that really didn't help.
 
@PedroTamaroff don't praise poor answers either, poor being iffy ones that use "it is obvious" to sidestep doing a proof.
 
Huy
@AlecTeal: This site is designed to reward experts more than learning people - because it's about answering questions which often need a lot of knowledge. If you're a learning person, why do you put so much emphasis on your rep anyways?
 
1:39 PM
It is also slightly annoying that you keep telling me what I think or do. "You need to stop treating..."
 
@Huy it's not rep that's important, it's the act of getting rep.
It's like a "well done :)" on homework.
 
I think everyone put me on ignore which is pretty crap
 
Huy
@AlecTeal: Why is the act of getting rep important to you?
 
It's not like the ring of power and Smeagal.
 
Well, @Alec, if people think it's not well done, it's not.
 
1:40 PM
@Huy don't deflect this onto me. Nice try though.
 
@beginner If someone's ignoring you, it's not me.
 
Huy
This is all about you, you're the only one complaining, really, @AlecTeal.
 
@Pedro You are a troll lol
 
@Huy the others cannot chat here due to lack of rep.
 
@beginner Whu...?
 
Huy
1:41 PM
@AlecTeal: One needs 20 rep to chat, afaik.
 
@pedro I talked to you 100 times above
 
Great answer, has 0 upvotes, I've given one just now.
 
@beginner Oh. I was too caught up with Alec. =)
 
Huy
@AlecTeal: If someone answers a question which attracts few people, obviously only few people will notice a good answer. That's just how it works.
 
@balarka I am not sure if I did it wrong, but was $z=(rc,rd)$ acceptable or do I need to use the $c^2+d^2=1$ thing still?
 
1:43 PM
I wrote a huge survey that only got 3 upvotes. [unnecessary off-topic whine]
 
@beginner I'm Argentinean. Does this answer your question?
 
Also, I found this question somewhere: mathb.in/25586. Does anyone know which "topic" does it fall into?
 
@Huy you're missing the point, look at the view count, it's not a far-fetched hypothesis to say: new questions are viewed MOSTLY by users.
 
@beginner I usually try not to be mean. Maybe the avatar is scaring you.
 
So of the lets say 10, but surely at least 5 people who viewed math.stackexchange.com/questions/1087435/… 1 upvote.
 
Huy
1:44 PM
@AlecTeal: Why don't you upvote the answer, if you think it's a great one?
 
LEL @Pedro
 
I am as I find them!
 
@AlecTeal That's a poor post.
 
Huy
@AlecTeal: Here's another great one, by myself, im my humble opinion: math.stackexchange.com/questions/1087332/…
 
@PedroTamaroff shush.
 
1:46 PM
@Pedro is a politician.
 
@AlecTeal Shushing me will definitely win this argument, eh! =D
 
@Huy nice time to get a few upvotes, ain't it?
 
Huy
@BalarkaSen: I'll upvote you if you upvote me!!!
 
no thanks
 
@Huy Let's not get into voting circles.
 
1:46 PM
@Huy that's how rep should be used.
[sarcasm]
 
@balarka responded to what he always considers nonnse hopefully he gets to my math hidden in there lol
 
Huy
@PedroTamaroff: You do recognise sarcasm when it's standing in front of you, do you?
 
Someone did not get this message.
12 hours ago, by Pedro Tamaroff
To all Avoid flagging things not flag-worthy. It creates noise.
 
@Huy I don't like the formatting, so no that is not a good answer.
 
Huy
@AlecTeal: Sorry about that. I'll reformat asap.
 
1:47 PM
JUMP THROUGH THOSE HOOPS
 
@Huy Not if it is written. There are no voice inflections in text. =)
 
If rep was worth something, I'd totally get it.
So usually @Huy on spotting that answer I'd think "I agree with this, and they've taken the time to write it, I want to encourage this behaviour" ad upvote.
Of course, I will play by your rules and think "You know that one sentence is to long" and not bother.
 
@beginner Did you read my responses?
 
looks around eh, might as well this
 
Huy
@AlecTeal: That is a really cool story, bro.
 
1:50 PM
:P
 
See I have a rule on a maths site: "I will not upvote any post that has 3 commas or more in one sentence" @Huy
 
@pedro yes sorry I dropped out
Am I the only one doing math lol. This noise is stopping @balarka from getting the will power to help me lol
 
/me looks @Huy with his QED face.
 
@BalarkaSen "pro(etale)-fundamental group", "profinite completion"? Tsk, tsk, tsk...
 
Huy
@PedroTamaroff: Hence why I used "!!!"
 
1:52 PM
Then you go around telling people they are studying backwards.
 
@pedro argentine is inamerica?
 
@beginner Argentina.
 
@beginner south America.
 
@PedroTamaroff Profinite completion is not really backwards.
 
As in the continent.
 
1:53 PM
I will be deeply offended if you cannot find it in a map.
 
IM YOUNG
 
Also he will be offended if you mention a certain Clarkson.
 
Profinite groups are fundamental stuff that should be studied before galois theory, @Pedro
 
Argentina is near Chile?
 
Yes
 
1:54 PM
From memory
(cheats because Chile goes along the whole side loo)
 
@beginner if it wasn't from memory why would you phrase it as a question
 
I am tired and I don't know what you just said
If it was from memory why wasn't it a question is the contrapositive or something but that still makes no sense
 
@PedroTamaroff Just saying' : Why not be a little open-minded and agree that big words doesn't mean the idea should be also big? Do you think profinite groups are THAT ahead of what I am studying?
Oh and there should have been a '?' mark after etale :P
 
I have to sleep I have been awake for 30 hours hehe
Yeah math makes lots of big words for simple things like graphs being the same is graph isomorphism
 
Also, @Pedro, if you read through the post, you'll see that I haven't included a single big word there. It's really a summary of my understanding.
And a very elementary write-up.
 
2:02 PM
Is the Schwarz inequality actually really useful and important?
 
@beginner Yes.
 
How can I remember it, what is it tellin me?
 
I'd really prefer you read the whole answer before making snide comments @Pedro. I have long abandoned pretending I know what I don't.
 
That the dot/scalar product can be bounded by the product of norms. @beginner
 
Oh okay that makes sense thanks @quid
 
2:05 PM
If you write it like |x.y| < = |x| . |y| it is easier to remember.
 
That is exactly how I will remember it :)
That is sort of a multiplication form of the triangle inequality ?
 
Great. Just make sure not to forget that |x| means the norm of the vector coming from the scalar product.
The analogy with triangle inequality is a bit vague, but yes notationally it is similar.
 
@BalarkaSen I have read all of it Balarka. Then why are you keeping that answer?
 
Actually I think I can prove the triangle inequality with the schwarz
 
"Then why are you keeping that answer?" I don't get it, why shouldn't I?
 
2:08 PM
Yes @beginner that is a main first use case of it.
 
@BalarkaSen You said "I have long abandoned pretending I know what I don't."
 
It might not be a good answer, as it's just a summary of my understanding, a note more like, but it answers the question.
@PedroTamaroff 'Cause I know most of what I said in the answer.
 
@BalarkaSen OK.
 
@pedro stepping on all the toes tonight lol
 
The last bit, about the connection of Galois theory with covering spaces and the dessins bit I don't know deeply, but I have heard about it from lectures some guys talked about here in the uni.
 
2:10 PM
@AlecTeal Just to clear things up, I hope you don't confuse my (personal) honesty with rudeness.
 
Personal honesty is often a form of rudeness
It is polite to lie
 
@beginner Hehe, if you're too sensitive everyone will be rude.
That's inevitable.
 
@PedroTamaroff I have no problem accepting what I don't know. I don't know the modern aspects of Gal(\bar Q/Q). Don't know about the stuff Grothendieck did. That's why I didn't write it.
 
@AlecTeal I usually try to help new users, for example:
Many exercises are like this: one carries into another, in increasing (or not?) difficulty. Personally, I would keep reading Spivak, and give it more time if necessary. You're always invited to drop by the chat and clear out any doubts or request help. — Pedro Tamaroff ♦ yesterday
 
Yeah rudeness is subjective
 
2:13 PM
@BalarkaSen can u help me?
 
depends, @iwriteonbananas
what's the question?
 
@PedroTamaroff sure you do.
 
@BalarkaSen The cone $CX$ is locally connected $\iff$ $X$ is locally connected
 
@iwriteonbananas Define "locally connected".
 
"X is"...?
 
2:15 PM
@PedroTamaroff it means the space admits a basis of open connected subsets
 
@iwriteonbananas Aha.
 
Never heard of "locally connected".
Thought it was locally simply connected.
 
@BalarkaSen do you like cool clipboards?
 
if $\mathcal{B}$ is a basis of open connected subsets of $CX$, we can just take $\mathcal{B}\cap X$ as a basis of open connected sets for $X$, right?
 
@iwriteonbananas So where are you getting stuck?
 
2:16 PM
which would prove one implication
what about the other implication tho?
 
Well $(\Leftarrow)$ part is not hard.
 
@iwriteonbananas How do you know $\mathcal B\cap X$ consists of connected sets?
 
@alec how are you?
 
You saw me a few minutes ago
 
@PedroTamaroff hmm good point i guess
@BalarkaSen how do u do it?
 
2:18 PM
@iwriteonbananas Tell me the definition of $CX$
 
@PedroTamaroff math.stackexchange.com/a/1087558/66223 this answer here, the OP and I agree "induction" in the comments, I preform the inductive step, why would I spend more time on this when the required part he was stuck on is entirely there
Do you see my point
 
@BalarkaSen $(X\times [0,1])/(X \times \{0\})$
 
Right. Now product of locally connected sets is connected.
 
@AlecTeal You uploaded a picture as an answer.
 
is the quotient map an open map btw.?
 
2:19 PM
Answers are to be TeXed.
 
if it is, i can use a previous result
 
That's known, Alec.
 
Huy
@AlecTeal: You have a mistake in your calculations.
 
@beginner Please don't do that.
 
@BalarkaSen hmm
 
2:20 PM
The first or second thin I said??
 
@beginner All of it.
=)
 
Or both?
Ok sorry
 
You see it is not sensible to post that right?
 
I'd think image of a locally connected set under the quotient map is locally connected
 
One of them yes
Oh wait yeah maybe sorry my bad
 
:) @iwriteonbananas
 
@BalarkaSen but the image of a open set need not be open under the quotient map
 
Does my page reloading mean I was banned?
 
@beginner No.
 
@iwriteonbananas Err, you're kind of right.
 
2:24 PM
Are clopen sets real?
I mean are they a joke?
 
No, they exist.
 
Huy
@AlecTeal: I found a second mistake in your "calculations".
 
lol that's awesome
 
@Huy okay cool.
 
@alec its alright I liked your workings
 
2:25 PM
For example, @beginner, the null set is both open and closed in $\Bbb R$
 
@alec I would upvote but I can't click java things
 
is it true that the image of a locally connected space under a quotient map is again locally connected?
 
@bala is there a non-trivial example that is short?
 
I guess, but I am not sure.
 
2:26 PM
@beginner Sure. $\Bbb R$ in $\Bbb R$ is clopen.
 
@beginner consider the situation that you have two disjoint intervals and forget all other real numbers.
Like your space is [0,1] u [3,10] for instance.
 
Then [O,1] is closed in [0,1] u [3,10] but it is also open in [0,1] u [3,10] ( while it is not open in R)
 
Exact video @alec that made me think it was a joke, I love that so much
Let me think about this @quid let me just get the definitions
 
@beginner what's the definition of open set? "Neighborhood to all of its points" right?
So take the plane, and take any point, you can always stick an open ball around that point, thus neighborhood to all points (I assume you know that open balls are open, the proof is easy)
At the same time it's also closed, containing all it's limit points
DUH DUH DUUUUH
See closed and open are not defined as opposites, closed means "you can't escape it" like addition on the integers is closed, you cannot leave the integers @beginner
@Huy bugger off, you found a legitimate error
 
2:33 PM
@iwriteonbananas Actually it needn't be true that continuous image of a locally connected space is locally connected.
 
Huy
@AlecTeal: Why did you edit your message? ;-)
 
But I think it's invariant under identifications on the space.
 
@BalarkaSen yeah indeed
 
@beginner now "open" doesn't mean you can escape it, it means "neighborhood to all of it's points" so if I give you a point you can go alittle above and a little below, which is important for defining differentiability.
 
@BalarkaSen ok i'll try to prove it
 
2:34 PM
@BalarkaSen Example Wrap the real line in a spiral converging to $0$.
 
Spiral?
 
@beginner got it?
 
Like an archimedian spiral?
 
@alec yep but what dos closed mean now?
 
The graph r=1/\theta would work @BalarkaSen
@beginner read up, I already did closed.
 
2:36 PM
I didn't get limit points
 
@beginner take the interval (0,1) and the sequence 1/n, 1/n is always in (0,1) but the limit isn't!
Limit point = point that is a limit :P
 
@BalarkaSen A spiral converging to $0$. Not an Archimedian spiral.
 
Okay so here it is the lim inf is 0
And that lim inf is the limit point
 
@beginner lim sup = lim inf as it converges, so just limit
 
If you're talking about the kind of spiral I have in mind, then yes, it's not locally connected at $0$.
 
2:38 PM
Ok sorry yes true, I haven't done calculus sorry
 
@BalarkaSen Yes.
 
It's not calculus, but okay.
 
Yes, you should :P
Thank god, you got me confused.
 
Limits are not calculus??
 
@beginner no.
 
2:39 PM
Limits are calculus
 
Where's the calculus in 1/n -> 0
 
Limits with epsilon delta are analysis
 
@beginner you need Protter and Morrey's "A first course in Real Analysis"
/me hits @beginner in the face with the aforementioned hardback.
 
I have rudin but it is hard
 
Another example of a space that is connected, path connected but isn't locally connected is $[0,1]\times( \Bbb Q\cap[0,1])\cup \{0\}\times [0,1]$.
@beginner You could read Spivak.
 
2:40 PM
@beginner Rudin's is concise, it's good for revision.
 
@alec no why???
@alec I am going into grade 7 in three months, go easy on me please
 
There are a hell load of example of spaces which are connected, path connected but not locally path connected
 
@beginner hit you with the book? Analysis hit me like a shovel, and hitting you with a shovel would be unrelated.
@beginner oi! Be proud! I'm not taking your age into account!
 
ok
 
analysis is alright
 
2:42 PM
I haven't got the standard math training so I feel a little wonky hehe
And I am in trouble for my friends rail gun so tomorrow is going to be hell, but I better sleep now
Thanks @alec @pedro @balarka for your help at various times in the last 10 hours
 
YW
 
@Pedro Exercise for you : Give an example of a path connected and locally path connected space that is not locally simply connected.
 
What does simply connected mean?
 
@Studentmath A space X is simply connected if every loop based at points of X is contractible. If you don't know homotopy, it's a bit hard to formally define it.
 
Don't know Homotopy yet
 
2:54 PM
@Studentmath If you have a two paths $\sigma_1, \sigma_2 : [0, 1] \to X$ in a topological space X with same basepoints, i.e., $\sigma_1(0) = \sigma_2(0) = x_0$ and $\sigma_1(1) = \sigma_2(1) = x_1$ then these two paths are said to be homotopic if there is a map $H : [0, 1]^2 \to X$ such that $H(0, t) = x_0$, $H(1, t) = x_1$ and $H(s, 0) = \sigma_1$ and $H(s, 1) = \sigma_2$.
i.e., you have a square and you're squeezing the two sides of the square so that the two sides go to a point
and the upper edge and the lower edge map to the two paths
 
Hah, interesting - I should get to it in about a month, I think
 
Could you take a look at this integral?

$$x=\sin y \Rightarrow dx=\cos y dy$$



$$\int \frac{1}{\sqrt{1-x^2}}dx=\int \frac{\cos y}{\sqrt{1-\sin^2y}} dy=\int \frac{\cos y}{\sqrt{\cos^2y}} dy=\int \frac{\cos y}{|\cos y|} dy$$
Is it right? How could I continue?
 

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