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Nov
21
comment Continuous function on a compact metric space is uniformly continuous
@shilov You should look at the last line of the proof. The inequality should explain it.
Nov
20
awarded  Nice Question
Nov
12
awarded  Nice Question
Nov
7
revised Reals constructed from equivalence classes of Cauchy sequences of rationals.
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Nov
7
revised Upper bound for order of finite group given relations
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Nov
6
answered Why $ \lim_{x\to \infty} -2xe^{-x/2}$ is $0$?
Nov
6
revised Why $ \lim_{x\to \infty} -2xe^{-x/2}$ is $0$?
edited title
Nov
3
comment Fourier transform of the characteristic function
@user929304 I see. I don't know if it makes sense, this is beyond my modest knowledge of Fourier transforms. It's not very useful but: Surely the decaying properties of $\mathcal F (\chi_{[c,d]}$ and $\mathcal F (\chi_{[0,1]}$ are almost identical?
Nov
3
comment Fourier transform of the characteristic function
@user929304 It's not clear to me what you mean. For example, "not differentiable in the usual sense" -- well apart from the points $c,d$ its derivative is 0, or am I missing something? And as for the FT of $\chi_{[c,d]}$: It looks to me like it's decaying. The expression is term one minus term two where each term is of the form one over something exponential times linear. But I might be missing something, it's been a while.
Nov
3
comment invertibility in C*-algebra
I don't understand why you would try to prove that $a-\lambda$ is invertible if by assumption ($\lambda \in \sigma (a)$) it isn't. What is your question?
Nov
3
comment Is it true that $\mathbb{Q}(\sqrt{3},\sqrt{7})=\mathbb{Q}(\sqrt{3},\sqrt{21})$?
Related: math.stackexchange.com/q/93463/5798
Nov
2
awarded  Nice Question
Nov
2
comment Proving $2\mathbb Z$ is maximal ideal of $\mathbb Z$
@RobertoMilandro Yes, exactly.
Nov
2
revised Proving $2\mathbb Z$ is maximal ideal of $\mathbb Z$
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Nov
2
answered Proving $2\mathbb Z$ is maximal ideal of $\mathbb Z$
Nov
2
comment Proving $2\mathbb Z$ is maximal ideal of $\mathbb Z$
Regarding your second sentence: It's not possible for any ideal in $\mathbb Z$ to have more elements than $\mathbb Z$.
Nov
1
revised Prove that $|S_1\times S_2|=|S_1|\times|S_2|$
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Nov
1
revised Extension of an analytic function to the right half plane
added 24 characters in body
Oct
31
awarded  Notable Question
Oct
31
answered How to find the span of a set of polynomials