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7h
answered “Cohomology classes correspond to homotopy classes of maps to Eilenberg Maclane spaces” and cup product?
7h
answered Is a finite cyclic group a Poincare duality group?
8h
revised When does reducibility over $\mathbb{Z}_n$ imply reducibility over $\mathbb{Z}$
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8h
answered When does reducibility over $\mathbb{Z}_n$ imply reducibility over $\mathbb{Z}$
9h
awarded  Nice Question
12h
answered $G$ a group and $H$,$K$ subgroups, $kHk^{-1} \subseteq H \implies kHk^{-1} = H$?
14h
comment Making sense out of the definition for “morphism of geometric spaces”
It's debatable whether you know what a sheaf is if you don't know what a homomorphism of sheaves is... anyway, yes, a homomorphism of sheaves is a natural transformation. If $f : X \to Y$ is a map of spaces, there is an induced adjunction $f^{\ast} \vdash f_{\ast}$ between their categories of sheaves; the left adjoint $f^{\ast} : \text{Sh}(Y) \to \text{Sh}(X)$ is called pullback or inverse image, and the right adjoint $f_{\ast} : \text{Sh}(X) \to \text{Sh}(Y)$ is called pushforward or direct image. All of this is part of what it means to know what a sheaf is; details are on e.g. Wikipedia.
14h
comment Making sense out of the definition for “morphism of geometric spaces”
For what it's worth, the standard term is locally ringed space (en.wikipedia.org/wiki/Ringed_space). Do you know what a sheaf is, and what a homomorphism of sheaves is? If not, it seems like you should learn this more basic material first.
15h
revised When is there a submersion from a sphere into a sphere?
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16h
revised Existence of submersions from spheres into spheres
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16h
asked When is there a submersion from a sphere into a sphere?
16h
comment Existence of submersions from spheres into spheres
@Mike: thanks for editing in the details about $S^2 \times S^1$! I edited in a generalization of the argument in my answer.
16h
comment Existence of submersions from spheres into spheres
@Travis: I went ahead and edited in the generalization.
16h
revised Existence of submersions from spheres into spheres
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16h
revised Existence of submersions from spheres into spheres
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16h
revised Existence of submersions from spheres into spheres
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16h
revised Existence of submersions from spheres into spheres
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18h
comment why this field is either $\mathbb{R}$ or $\mathbb{C}$?
In the second statement, you're missing the hypothesis that the topology on $K$ is locally compact (encyclopediaofmath.org/index.php/Topological_field); otherwise there are counterexamples. I don't understand the first statement at all.
1d
awarded  Nice Answer
1d
comment Let $k$ be an algebraically closed field and $Y \subset \mathbf{A}^n$ be the set $\{(t,t^2,t^3|t \in k\}$. What is are the gnerators of $I(Y)$
Oh, hmm. I might've been thinking of a higher-degree example.