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May
30
comment Can you compute relative homology using simplicial chain complex?
Sure — if you know (or believe in) the result for absolute homology, just apply 5-lemma to the long exact sequence for the pair $(M,\partial M)$.
May
30
comment Logic behind cubic resolution of $x^4+px^2+qx+r=0$
...Maybe Dummit & Foote, ch. 14 (see esp. sec. 6–7) is not a bad reference (but I hope someone will give a better reference)
May
30
reviewed Close $\hom_R(A,B)$ is finitely generated if $R$ is noetherian
May
30
comment Logic behind cubic resolution of $x^4+px^2+qx+r=0$
Yes, there is some logic behind it — it is explained by Galois theory...
May
29
reviewed Close Group internal automorphisms
May
29
comment Elementary proof that $Gl_n(\mathbb R)$ and $Gl_m(R)$ are homeomorphic iff $n=m$
related (essentially duplicate of?): Elementary proof that $\mathbb{R}^n$ is not homeomorphic to $\mathbb{R}^m$
May
29
comment Why is $\sum\limits_{k=0}^{n}(-1)^k\binom{n}{k}^2=(-1)^{n/2}\binom{n}{n/2}$ if $n$ is even?
I don't see how Hagen von Eitzen's answer is any different from the first of two proofs by Marc van Leeuwen there — but if this helped you — great.
May
29
reviewed Close Sheaf of ideals
May
29
reviewed Close To prove this sequence does not contain a perfect square
May
28
comment On what sets can $\mathfrak{S}_n$ act transitively?
Calling this 'complete classification' is an overstatement, IMHO (just an equivalence of two classification problems).
May
27
reviewed Close Proof of an infinite series formula
May
27
reviewed Close $\exists \implies \forall$
May
27
reviewed Close find p,q to the expression A does not depend on x?
May
27
reviewed Leave Open What is the moduli space of lines in $\mathbb R^3$?
May
27
reviewed Reopen Find all functions $f$ such that if $a+b$ is a square, then $f(a)+f(b)$ is a square
May
27
comment Prove $\sum_{n= -\infty}^{\infty} \frac{1}{(t+n)^2} = \frac{\pi^2 }{\sin^2(\pi t)}$ using f(x)=1-|x| and Poisson summation formula
Related: Showing $\sum_{n=-\infty}^\infty \frac{1}{(z+n)^2}=\frac{\pi^2}{\sin^2(\pi z)}$ & $\sum\limits_{k = - \infty }^\infty {\frac{{{{\left( { - 1} \right)}^k}}}{{a + k}} = \frac{\pi }{{\sin \pi a}}} $
May
27
comment Spin manifold and the second Stiefel-Whitney class
@QiaochuYuan Sure (the only difference is the first sentences, essentially ;-)
May
26
revised Spin manifold and the second Stiefel-Whitney class
texified
May
26
answered Spin manifold and the second Stiefel-Whitney class
May
26
comment Spin manifold and the second Stiefel-Whitney class
Related: Which manifolds are parallelizable?