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olivier dot begassat dot cours at gmail dot com


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awarded  Popular Question
Jan
20
comment $\alpha \in \mathbb{C}$ with $[\mathbb{Q}(\alpha) : \mathbb{Q}] = 2^k$ but $\alpha$ inconstructible
But $\zeta_6\cdot\sqrt{2}$ manifestly is constructible with a straight edge and a compass.
Jan
20
comment $S^1$ a p-local complex?
What about the usual reduced homology? $H_*(S^1)\simeq\Bbb Z[1]$ is a copy of the integers in degree $1$.
Jan
20
revised Conceptual doubt in a theorem in Group rings
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Jan
20
answered Conceptual doubt in a theorem in Group rings
Jan
20
comment Laplacian and Hodge Laplacian
The Sobolev space of functions is just the Sobolev space of sections of the trivial line bundle.
Jan
20
comment Laplacian and Hodge Laplacian
I take it the Laplacian you talk about in the beginning is defined for real or complex valued functions, but you can define a Sobolev space of $p$-forms, and more generally, Sobolev spaces of sections of vector bundles.
Jan
20
answered Are $(l^1, \|.\|_2)$, $(l^2, \|.\|_3)$ Banach spaces?
Jan
20
comment Orbits of left-multiplication from $\mathrm{PSL}_2(\mathbb Z)$ on $\mathbb Z^{2\times 2}$
$SL_2$ acts on the left, not $PSL_2$.
Jan
19
comment Prove: $\int_0^1 \frac{\ln x }{x-1} d x=\sum_1^\infty \frac{1}{n^2}$
In case anybody reads this answer, I think it is necessary to say something like for all $u\in(0,1)$ and for all $n\in\Bbb N$, $$\left|1+\frac12u+\frac13u^2+\cdots\frac1nu^{n-1}\right|\leq-\frac{\ln(1-u)}u=g‌​(u)$$ so that, since $g$ is integrable on $(0,1)$, one can apply dominated convergence, and swap the sum with the integral.
Jan
19
comment Prove $F^2_{n+1} - F_nF_{n+2} = (-1)^n$
AlexR is correct!
Jan
19
revised Quotient space of $S^n$ and the projective plane
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Jan
19
comment Quotient space of $S^n$ and the projective plane
I doubt it: I don't thinkthe mapping cylinder is orientable when $n$ is even.
Jan
19
revised Quotient space of $S^n$ and the projective plane
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Jan
19
answered Quotient space of $S^n$ and the projective plane
Jan
19
revised Mapping torus with homotopic homeomorphisms
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Jan
19
comment Mapping torus with homotopic homeomorphisms
@YonKim corrected the formulas.
Jan
19
revised Mapping torus with homotopic homeomorphisms
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Jan
19
comment Ext groups due to Yoneda: why is this class zero
Are you sure those modules are projective $\Bbb K[x]$-modules?
Jan
19
answered Big list of “guided discovery” books