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12:00 AM
instead of the lowercase d?
 
Yeah.
 
Thanks
 
@JacobSchlather Anything further I can tell you about the axiom of choice?
 
I think that covers what I was curious about.
Thanks
 
Well, I'd be glad to answer anything else you have in mind. It is my research area, after all :-)
 
12:04 AM
Well
 
There only 9 homeworks left to grade!
 
I was proving the equivalent conditions for noetherian modules
recently
 
Dependent Choice is needed :-)
 
that's what I used
I was curious though
if you assume those three conditions are equivalent
can you get any sort of choice function
 
Which three?
 
12:06 AM
Let M be a module over a commutative ring with a unity.
1) Every submodule of M is finitely generated.
2) Every ascending chain of submodules terminates.
3) Every collection of submodules has a maximal element under inclusion
 
Well. To prove any real consequence of this equivalence you'd need to show that every power set can be made into a Noetherian module over some commutative ring.
 
Well
I guess none of those conditions are first order theories
 
In ZF it is meaningless when discussing sets.
 
Well I wanted to use lowenheim skolem
 
However, since every module is a group, this means that every set can be given a group structure. This last one is equivalent to the full axiom of choice.
 
12:10 AM
yeah
 
Not all is lost, though. It is possible that you can get from this equivalence that for sets which can be given a group structure you can define some choice function.
 
It is an interesting question, I'll have to think about it for a while.
 
dependent choice for sets with group structures
:P
I guess though you need to give each set an abelian group structure
and then define a ring action on it so that it's a noetherian module
 
12:24 AM
@AsafKaragila Thanks for the enlightening conversation, I'm going to do some work or sleep. I'm leaning towards the latter.
 
@JacobSchlather Sure. :-)
I suppose I'll go to sleep as well.
 
12:54 AM
Isn't it ironic? The axiomatic system known as "New Foundations" does not have an axiom of foundation :-)
 
QED
hehe
 
Either way, now I'm really off to sleep. Ciao.
 
They haven't gotten around to constructing one?
 
1:29 AM
@AsafKaragila Good night.
@JM I wonder if it exists under another name
 
1:40 AM
Hmm, anyone able to help with this Q: imgur.com/THaJk
 
@Matt What's bothering you about it?
 
Well, am I correct with which rows and columns are associated?
since C_s(s,t) t is treated as a constant
 
Is that your answer in the image?
 
Yes
There is an additional answer I still need to figure
 
I don't know if I would say that the association is with rows or columns, but definitely, dC/ds measures the change along each column and dC/dt measures the change along each row.
Perhaps that is what they are trying to ask (kind of poorly in my opinion)
 
1:49 AM
Yea, theres obviously an association between everything in that table
lol
 
As to which has a greater effect on the wind chill, that depends on the units you are using.
 
Surely we cane assume the units in the table are to be used
 
I dislike how essays/articles/books/etc. are titled "How X" (where X = some mysterious phenomena, or human activity the public is ill-informed about, etc), but the major thesis is actually establishing X exists in the first place (and implications of it, and so forth) - rather actually explaining or describing the mechanisms responsible for X. Very important semantic distinction.
 
mph and degrees
 
you're comparing miles/hr against degrees F
how can you compare them?
is 1 mph greater than 1°F?
 
1:51 AM
No, you dont understand the question
 
The question seems sort of meaningless.
Okay. I guess I don't
 
C is a function of S and T
 
So you are assuming that 1mph=1°F for the sake of comparison.
 
Yes
 
Then I would ask does T or S have more effect on the wind chill, not dC/dS or dC/dT
dC/dS is how much effect S has on C
dC/dT is how much effect T has on C
 
1:55 AM
hmm yea
That would make more sense to ask
 
I think the wording of the question is suspect :-)
 
I think it reads
 
They may mean what we have discussed here, though
I think
 
"Can you determine from the table if the change in speed or change in temperature has a greater effect on wind chill"
 
That is exactly what I think they mean.
 
1:57 AM
I dont know if we can tell from that table though
 
look at dC/dT and dC/dS over the table, I don't think it is clear.
at 0 mph, dC/dT = 0
I am assuming the C is the difference in the temperature.
 
C is wind chill
what it feels like when the temperature is accompanied by some wind speed
 
Is that the difference between the value in the table vs T?
So the wind chill is not the chill, but the perceived temperature?
 
No, the wind chill is what temperature it feels like
the temperature is the actual temperature
 
That would be the perceived temperature
 
2:01 AM
Right
 
1 min ago, by robjohn
So the wind chill is not the chill, but the perceived temperature?
correct?
 
correct
 
It makes a difference in dC/dT, but not dC/dS
in dC/dT it means a difference of 1
because using that definition of wind chill, dC/dT = 1 at 0mph
 
hmm
 
at 15 mph, it varies between 1.6 and 1.3
And dC/dT is unitless.
Then just compute dC/dS over the whole table in °F/mph and compare I guess.
I have to take my dog to the park. If you still want to talk later, we can.
 
2:12 AM
AH ok
Calculated the change when holding each item constant
Ill post it
 
2:37 AM
can anyone answer to my question: math.stackexchange.com/questions/87222/…
 
2:55 AM
@Victor What's wrong with Sasha's answer?
 
- Is it possible that Victor posted this comment before Sasha's answer?
 
3:06 AM
They were posted at about the same time.
 
@robjohn - Someone have use more effort to give the more complete solution, so i am willing to give the points to that people
 
Do you want a more detailed answer?
Oh, I see. Sivaram has posted a more detailed solution. Of course, it goes without saying that you can accept any answer that you feel helped you most, @Victor.
 
Sasha's answer is pretty complete, but you do have to know the binomial theorem, to start with.
@Srivatsan I will look.
They are all based on the same idea, but more steps are included in Sivaram's answer.
 
3:24 AM
@robjohn - actually Sasha have skipped some step that is important to me...
 
QED
good evening
 
Good evening, QED.
@robjohn I was going to comment that you should've posted that answer in the "original" question. Any guesses why I didn't post that? ;)
 
4:43 AM
@Srivatsan I am unsure of which "original" question is meant here.
 
Sorry if that wasn't clear. I tried to make it a bit vague: ends up too vague as usual =)
 
:-)
 
I was going to comment that you should've posted it here instead of the dup.
But then on checking the original question, I found that Mike's solution is identical to yours =)
 
Ah, I've mentioned that we handle combinatorical problems similarly.
 
You have? Update: I see no such sentence in your answer.
 
4:52 AM
I have. The difference being he gets 20 votes for it ;-)
 
QED
hmmmm
0
Q: How to prove that the limit of an $n$-gon is a circle?

qqqqqqqqqqqqqqqquqqqqqqqqqqqqqHow does one prove that a regular $n$-gon with perimeter $1$, approaches (becomes) a circle as $n$ goes to (or if $n$ is) infinity? It is not enough to prove that all points become equal distance to origin, since this also holds for the limiting object of the graph of largest area drawn on the s...

this is bugging me
> the graph of largest area drawn on the square graph and enclosed by a circle as we make the squares smaller and smaller.
 
Do you agree with my comment, QED?
 
QED
yes
I think he should have included the picture
that pi = 4 joke
it's very hard to tell what he actually wants
and it doesn't help that I didn't actually read the question
 
@robjohn If it's any consolation, I upvoted yours (long time back), but not Mike's. That answer is swimming in votes already, so he won't miss mine I imagine... =)
 
QED
why does the squares thing not tend to the circle but the polygon does
 
4:54 AM
@QED You could link to that previously asked question.
 
QED
I think he's actually wrong about that
 
@QED he - who? The OP?
 
QED
qqqqqqqqqqqqqqqquqqqqqqqqqqqqq
I think he's starting off with a false assumption
 
@QED By "tending to the circle" do you mean the length of the boundary?
 
QED
I think it's meaningless
 
4:57 AM
I think the common assumption here is that the sequence is tending to a circle of radius 1/tau, so that the perimeter is 1.
 
QED
he is saying:
* the sequence of polygons tends toward the circle
* the sequence of boxes (pi = 4 thing) doesn't
 
pointwise they both do, but not in C^1
 
QED
he's probably basing that on the length of the curve tending towards the circle
 
@robjohn What does pointwise convergence mean for a sequence of polygons? As QED wrote, Hausdorff metric makes sense, but we should be a bit careful in defining the sequence of polygons.
 
For regular polygons, I already hinted at Archimedes. I only hope he bothers to actually do a search. "Help yourself" and all that.
 
QED
4:58 AM
pointwise?
 
not only does gamma(t) need to tend to the circle, but gamma'(t) needs to tend to the tangent of the circle.
If you want the arclength to tend to pi x diameter
 
QED
wait so if gamma_n is the sequence of polygons.. it does tend towards the circle?
 
gamma_n (t) will be the point on the n-gon, right? How exactly do we define that?
@QED We not sure, I believe.
 
QED
I was just thinking about Hausdorff distance of the point sets, with that point of view the 'perimeter' is a red herring
 
@Srivatsan what do you mean? how do we define the derivative?
 
QED
5:04 AM
on the other hand we can view these things as piecewise differentiable curves (gamma(t))
 
@QED that's the way to do it.
 
QED
we could probably construct one that tends towards the circle as a point set, but whose length diverges
 
Quick question that came up in my reading: how does one prove that if U is simply connected in the complex plane and if there exists a continuous bijective function mapping U to V, then V is simply connected. Obviously since they are homemorphic it should be preserved, but how does one prove this?
 
@QED not if the derivatives of the approximant approximates the circle, too.
 
QED
now this question has made me think of an interesting thing
hmm
lets say gamma_n is the sequence of polygons and kappa_n is the sequence of boxes (pi=4 thing)
it's not true that gamma_n(t) - kappa_n(t) tends towards zero is it?
that's how their derivatives can differ so much, right?
 
5:07 AM
We can just push all the homotopies though the map, right?
 
@QED they can tend to 0 and still have the derivative diverging.
 
QED
I don't understand how that is possible
interesting though
how could gamma_n(t) - kappa_n(t) tend to zero but gamma'_n(t) - kappa'_n(t) not?
maybe it almost everywhere tends to zero?
32
A: Is value of $\pi$ = 4?

TCLThis problem illustrates the fact that two functions can be very close: $|f(x)-g(x)|<\epsilon$ for all $x\in [0,1]$, but their derivatives can still be far apart, $|f'(x)-g'(x)|>c$ for some constant $c>0$. In our case, let $x=a(t),y=b(t),0\le t\le 1$ and $x=c(t),y=d(t), 0\le t\...

let gamma_n converge as a point set to { gamma(t) in R^2 | t in R }
Suppose for all epsilon > 0, there exists n such that gamma_n is within epsilon of gamma (as a point set). Then for what proportion of the curve is it possible that gamma'_n - gamma' > c?
I think that proportion goes to zero?
maybe not
 
5:25 AM
@QED that is just what is happening in the box-circle thing
Oct 20 at 23:16, by robjohn
He and I seem to attack combinatorial problems in the same way.
@Srivatsan that is the conversation I was talking about
 
QED
what is
I don't know how to answer my question
it's not necessary to smooth the corners
 
Take the simpler example of the staircase tending toward the diagonal of a square.
It is necessary make the sides of the boxes parallel to the circle.
or the diagonal of the square.
 
QED
gamma'_n(t) = (1,0) or (0,1) for the staircase
gamma'(t) = (sqrt(2)/2,sqrt(2)/2) for the diagonal
 
that is why we parameterize by arclength; to prevent that
 
What rob said.
 
QED
5:30 AM
oh
 
you try to match the parameter values so that the gamma(t) = beta(t) and gamma'(t) =beta'(t)
 
QED
that's the arc-length parametrization then
 
at least the same parameterization so that gamma'(t) !=0
but arclength is the standard.
 
QED
sqrt((sqrt(2)/2 - 1)^2 + (sqrt(2)/2)^2) = sqrt(2 - sqrt(2))
 
formulas become simpler when using arclength
 
QED
5:32 AM
so if we put c anything below sqrt(2 - sqrt(2))
 
Hence the other name "natural parametrization".
 
QED
even though gamma_n - gamma (hausdorff distance) tends towards zero, gamma'_n - gamma' > c for the entire curve
 
@QED it can happen
 
QED
what can happen?
anyway that staircase example is nice because it shows I was completely wrong about proportion tending towards zero
 
gamma_n - gamma (hausdorff distance) tends towards zero, gamma'_n - gamma' > c for the entire curve can happen
@QED: consider the curve gamma_n(t)=(t,sin(nt)/n)
tends pointwise to (t,0), but gamma_n'(t) does not converge
 
QED
5:47 AM
even neater!
 
6:15 AM
Hello there
 
 
1 hour later…
7:37 AM
Morning! @AsafKaragila: Thank you very much, I'm going to read your answer now.
 
7:58 AM
@robjohn You commented in your answer to the question "How to prove this particular limit as x->0 (sin x ) / x = 1" "understood, to be proven later". In any definition, there will be things that are left as understood. & a little bit of hand-waving can make believable... These are excellent examples of a recurring theme in mathematics found from the earliest elementary school days all the way up through Calculus and beyond...
 
8:08 AM
@Matt You made me get out of bed.
I'm a bit sick, so I've decided to skip the one class of algebra for today.
 
@AsafKaragila Oh noes, hope you get better soon!
 
So you can ask me through the day, and I'll likely to be here to answer.
 
This sentence is ungrammatical.
 
It's just a minor flu. Very minor.
 
So when you write algebra, I assume it means you're lecturing abstract algebra?
 
8:11 AM
In my university I'm the only student in set theory. So there are not enough people to open interesting courses. Furthermore, I already took all the courses this university can offer.
I am still missing two courses for my degree. So I was forced to take courses in alg. top. and commutative alg.
 
Oh! I thought you were doing a PhD : )
 
That would be next year, I hope.
 
@AsafKaragila Luck you : )
 
Thanks.
 
Ok, so what is your answer to my second comment?
 
8:12 AM
I am 1 rep. point under Mike, that is so unfair.
Canonical names are interpreted the same under anything, this is why they are canonical :-)
 
Yes but there is no pair (x,q) in p!
So it should be emptyset instead of {p} as you wrote.
 
@AsafKaragila What do think of the comment: In any definition, there will be things that are left as understood. & a little bit of hand-waving can make believable..
 
(I'm talking about Jech{u})
 
Hah. Jech{u}.
 
: )
 
8:15 AM
@Skullpatrol I disagree with that.
 
@AsafKaragila Why?
 
@Matt You should ask that guy who wrote that book, then.
Because it would seem to me that canonical names are to be interpreted as they are under any condition.
 
@Matt Please feel free to comment on the comment
In any definition, there will be things that are left as understood. & a little bit of hand-waving can make believable..
 
And it seems to me that this notational nightmare that you use is exactly why I dislike this.
 
@Skullpatrol I heard you like comments, so I put a comment in your comment...
@AsafKaragila Ah. So this means that dot{x}[G] = x for any G?
 
8:20 AM
Yes.
 
Ha. Thank you!
 
Also, check{x} is canonical, dot{x} is just a name.
This is what you asked in your previous question, you see...
 
No, the other way around: dot{x} is canonical, check{x} is a name.
 
@AsafKaragila Where?
 
Again, depends on your notation.
The Jech-ian notation is that check goes for canonical names, dot goes for general names.
@Skullpatrol In here.
 
8:22 AM
So assuming it's the other way around, where dot{x} stands for the canonical p-name and check{s} stands for any old p-name, then dot{x}[G] = x for any G?
 
phew
 
This is your previous question, in a nutshell.
Canonical names are forced by 0, therefore every filter interprets them as such.
 
But G is an arbitrary set, not necessarily a filter. In my second question for example, G = {q}.
So there is no 0 to force anything...
 
Which is why I am not sure about that.
In practice there is absolutely no use of interpretation by "sets".
Furthermore, you can talk about things that p forces.
That is, things which will be interpreted as true whenever p is in the generic.
Even then you have some sort of continuity, and 0 forces what it should force.
 
8:26 AM
I don't know what "the generic" is.
 
The generic filter that will be used later on.
 
Ah.
 
It is one of the equivalent definitions for forcing.
p forces phi IFF for every generic filter G such that p in G, V[G] models phi.
 
Yes but the problem is that {q} is not a filter...
 
@AsafKaragila Would you agree with the comment: In any BASIC definition, there will be things that are left as understood. & a little bit of hand-waving can make believable..
 
8:28 AM
Which makes this exercise even more confusing.
@Skullpatrol I disagree again.
 
So what should I do about dot{p}[{q}] ? You say it's {p} and I think it should be the empty set...
 
Which brings us back to the matter of how you want to interpret this question, and why you should contact whatshisname.
 
Ok. This makes me want to cry.
 
Why? Emails are mostly harmless.
 
@AsafKaragila They have uploaded a new version of the assignment.
A typo free one.
Where they have inserted 0 in this question whenever needed.
 
8:31 AM
@AsafKaragila At the very basic level there must be certain undefinable elements
that a little bit of hand-waving can make believable.
isn't that the essence of doing mathematics?
 
@AsafKaragila: I'm sorry. Without the typos I think the question is clear to me, so I've badgered you for nothing : (
 
That don't look right.
That don't look right at all.
 
@Matt Nah. It's fine,
@Skullpatrol No.
 
@AsafKaragila What would you consider then the essence of doing mathematics?
 
@Skullpatrol Thinking.
@Matt May I see that assignment?
 
8:38 AM
@AsafKaragila But you need something to think about
 
Yes. The definitions.
 
@Skullpatrol There are several points of view about this. Euclid for example thought that mathematics could be divided into arithmetic and geometry and that was it.
@AsafKaragila Sure
 
@Matt Euclid is the one who started with undefinable "points" and "lines"
 
@Skullpatrol Then there was the point of view that mathematics is about taking a set of axioms and then deduce theorems based on those axioms regardless of whether the axioms and the deduced things could actually be true in reality.
 
@Matt So you see, I was right after all :-)
 
8:40 AM
@AsafKaragila Yes : ) I like. Now I'm less confused.
 
If you will correct your question, I will correct my answer. If not, do note there that there was a typo in the source because otherwise people can argue about my answer :-)
 
I think I'll do the latter : )
 
@Matt Again " a set of axioms" are undefinable just like "points" and that a little bit of hand-waving can make believable.
 
@Skullpatrol Not if you're an intuitionist.
 
Even if you're not.
Sets of axioms are syntactical objects, you should treat them as such and "Go Wittgenstein".
 
8:45 AM
At the very basic level there must be certain undefinable elements
that a little bit of hand-waving can make believable.
this is the essence of doing mathematics
 
@Skullpatrol Why "must"?
@Skullpatrol Can you define "essence", please?
 
@Matt "must" because we need a starting point and essence is undefinable ;-)
just ask any philosopher
which I am not
 
Philosophers know squat about mathematics.
 
@AsafKaragila Did Wittgenstein know squat about mathematics?
I don't know much about his work, but he had issues with language right?
 
He studied under Frege and Russell, however he found mathematics irrelevant for philosophy since it is composed only of statements of "assume ... then ..." which can be vacuously true, and without much content.
 
8:54 AM
@AsafKaragila So it was Frege and Russell that had issues with the connection between language and thought?
 
I don't know.
 
@AsafKaragila In my humble opinion mathematics is a very specialized bridge between language and thought... what do you think?
@Matt What do you think?
 
I am agnostic about these things. I focus my energy on mathematics, rather on its philosophical interpretations and implications. I did that during my undergrad and that led me nowhere interesting really. You always get stuck at the dogmatic stage that one has to believe.
 
"the dogmatic stage that one has to believe" is exactly what I'm talking about in At the very basic level there must be certain undefinable elements
that a little bit of hand-waving can make believable.
 
I see no point for belief in mathematical practice.
 
9:01 AM
@AsafKaragila Are you saying that you don't have to believe in what you're doing?
 
No. Only to enjoy.
Belief, as a concept, is paradoxical and self contradictory. I do my best to avoid beliefs anywhere in life.
 
Believing in it makes it so much more enjoyable
and provides the motivation to memorize
 
I hate memorization. I need not be motivated to do that.
 
Some memorization is necessary though
 
No, it's not. Understanding is necessary.
 
9:06 AM
You won't understand it unless you believe in the implications that it leads you to.
 
@Skullpatrol Sorry, was having a shower. I can't argue about things that aren't defined.
@AsafKaragila I think it is. For definitions such as group, for example.
 
Not everything in life is defined
 
@Skullpatrol How dare you tell me what I will and won't be able to do? You don't even know me, let alone know what and how I know things. Who do you think you are, telling me these sort of things??
@Skullpatrol This is exactly why mathematics is not a part of life. It has its own accord, disjoint from this of life. Until you understand this, you can never really do mathematics.
 
@AsafKaragila I humbly apologize if I have offended you in any way :-(
 
We grumpy?
 
9:12 AM
No, just tired of pointless discussions involving "Define definition." recursively over and over.
 
@AsafKaragila Would you like to see the definition of recursive?
 
No. I would not.
 
Mathematics isn't philosophy. All things in math can be traced back to simple observable fact upon which everything builds.
 
@AsafKaragila He's a troll.
 
@AsafKaragila Look under "recursive" that is a joke
 
9:14 AM
@WillihamTotland Trace back Prikry Forcing.
 
@Matt and I'm not a troll
 
Of course you would say that.
 
@Matt why would you call me a troll?
 
Skullpa-troll : )
 
is there no connection between math/language/philosophy?
 
9:17 AM
There is a field called philosophy of mathematics, I think you might be interested in that.
 
@AsafKaragila I'd love to, if I understood the concept in the slightest, or even half the words used in the definition. :P
 
@Matt That is a reference to the Oakland Raiders
don't you recognize me avatar
on patrol for the quarterbacks skull
 
@WillihamTotland it's indeed not a trivial definition.
 
I had no idea. : ) I'm not into sports. Sports bore me. Watching as well as doing.
 
But unless I'm sadly mistaken, it relates to subsets sharing properties of their supersets, which makes intuitive sense.
Or possibly the other way around…
 
9:22 AM
Prikry forcing is a forcing which changes cofinality without collapsing cardinals. It requires large cardinals though.
 
@AsafKaragila Thank you for sharing your thoughts on these questions and again I apologize if I have offended you in any way.
@Matt I will look into the field called philosophy of mathematics, thank you
 
@AsafKaragila: Well, I have no idea if that is close to what I suggested or not.
But I'm guessing not.
 
Not too much :-)
 
Irrespectively, my point is that it's not based on some arbitrary definition somewhere; while certain aspects of mathematics may be unprovable, they are unquestionably true.
(Ref. Gödel's incompleteness theorems, etc.)
 
9:43 AM
What is ‘true’?
 
for all x, x\notin\varnothing :-)
 
Ick. That presume the language of set theory. I'd go with \bot \Rightarrow \bot myself.
 
Ick. That presumes some language in which \bot is a symbol.
 
I'd rather have \bot than \lneg. Then it's still meaningful even in the empty propositional language.
 
\lnot?
 
9:50 AM
Oh yes, that one.
 
@ZhenLin To say what is, that is,that is true; while to say what is not, that is, that is false ;-)
 
@Skullpatrol: I don't care for your quotes.
 
@ZhenLin So you recognize it as a quote?
 
No, but I can guess.
 
@JonasTeuwen: Hello : )
 
9:55 AM
@ZhenLin You did ask: What is ‘true’?
 
It wasn't directed at you.
 
@ZhenLin oh...
I misread you
 
Anyway, I have to go now. But do ruminate on the question.
 

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