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Jun
24
asked Reconciling two different definitions of constructible sets
Jun
19
reviewed Approve Isomorphism between $\Bbb{R}^2 \times \Bbb{R}^2$ and $\Bbb{R}^2 \otimes \Bbb{R}^2$
Jun
19
answered What are the rules of powers of powers?
Jun
19
accepted Can we see directly from the cocycle condition that 2-cocycles are symmetric?
Jun
19
comment Can we see directly from the cocycle condition that 2-cocycles are symmetric?
+1 Just the kind of thing I was looking for. Cyclicness enters the proof in the form of a descent argument!
Jun
19
revised Can we see directly from the cocycle condition that 2-cocycles are symmetric?
corrected a typo
Jun
18
asked Can we see directly from the cocycle condition that 2-cocycles are symmetric?
Jun
7
comment Prob. 6 (c), Sec. 10 in Munkres' TOPOLOGY, 2nd ed: Set of elements having no immediate predecessors in the minimal uncountable well-ordered set
Can you spell out why $A\subset S_\Omega$ countable implies bounded above?
Jun
6
revised Continuity and Uniform Continuity on half closed intervals
changed $b$ to $y$ to avoid overworking $b$ since it is also the endpoint of the interval.
Jun
4
accepted Embedding $G$ in a $Z(G)$ extension of $\operatorname{Aut}G$.
Jun
4
accepted Why is the cartesian product so categorically robust?
Jun
3
awarded  Good Question
May
29
awarded  Nice Question
May
29
asked Why is the cartesian product so categorically robust?
May
28
comment Ramification index of infinite primes
Prop 1.2(i) is easily salvaged by saying f=1 and e=2 for complex embeddings extending real ones, but (iii) and (iv) seem to me to require his convention...
May
28
asked An infinite prime can ramify right? (So what is Neukirch talking about?)
May
18
reviewed Approve Probability of event in join sample space of X & Y
May
16
comment Understanding the generator of $H_1 (S^1 \times I)$
Also, this question is closely related to the very first question I ever asked on this site: math.stackexchange.com/questions/50362/…
May
16
comment Understanding the generator of $H_1 (S^1 \times I)$
This kind of continuous map that is not invertible is really important to understand homology. For example, how do we know that a loop $k$ that goes twice around $S^1\times 0$ is homologous to $2h$? Because $2h-k$ is the boundary of a map from a single triangle into $X$ that squishes the whole triangle into $S^1\times 0$.
May
16
comment Understanding the generator of $H_1 (S^1 \times I)$
Yes, exactly. E.g. the map from the square to the cylinder obtained by gluing a pair of opposite edges together is a continuous map, but it doesn't have an inverse.