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Mar
31
comment Can flooring and ceiling thirds sum up to more than a whole?
By the way, wouldn’t a more elegant approach be to set the last column width to $x - 2·\lfloor x/3 \rfloor$ so the column widths will always add up to $x$?
Mar
31
answered Can flooring and ceiling thirds sum up to more than a whole?
Mar
31
comment What other classes of commutative rings can be defined by requiring that $\{0\}$ is the only proper ideal satisfying some condition?
How did you come up with the name orthic?
Mar
31
comment Want to show two smooth manifolds are diffeomorphic
It would also suffice to show that $f$ is bijective and has an invertible tangential at each point. Then the inverse function theorem implies that $f^{-1}$ is smooth.
Mar
31
awarded  Mortarboard
Mar
31
answered Kernel of biproduct projection is the other biproduct injection
Mar
31
comment Ring Homomorphism-fixed sets
Got any suspects?
Mar
31
comment How to find a basis of eigenvectors?
You mean like vectors $X_1’, X_2’, X_3’$ such that $ϕ_A(X_1’) = 0·X_1’$, $ϕ_A(X_2’) = 2a_1·X_2’$ and $ϕ_A(X_3’) = -2a_1·X_3’$ for example? Hm, …
Mar
31
comment From any ten naturals, find some numbers whose sum is divisible by $ 10.$
@yazhini Not quite. Imagine $a_1$ having the same remainder as $a_1 + a_2 + a_3$.
Mar
31
answered From any ten naturals, find some numbers whose sum is divisible by $ 10.$
Mar
31
revised Prove that G\S generates G
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Mar
31
answered Prove that G\S generates G
Mar
31
answered Is there any way to test the existence of left or right inverse matrix?
Mar
18
comment Topology related question
Welcome to the site. It’s much more the site’s etiquette to show one’s own effort to solve the stated problems and/or to give a little context.
Mar
15
accepted Can the cohomology ring of the two-fold torus be calculated abstractly?
Mar
15
comment Question about open mapping theorem
I think they are both true in general, but I’m kind of too lazy to prove it right now. I thought it’d work with the Lebesgue’s number lemma, but I’m not sure about that anymore.
Mar
15
revised Question about open mapping theorem
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Mar
15
comment Question about open mapping theorem
As $\mathbb D_2 ⊂ Ω = f(Ω)$, this isn’t a counterexample to (A) and (C).
Mar
15
revised Question about open mapping theorem
deleted 84 characters in body
Mar
15
answered Question about open mapping theorem