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Jan
10
awarded  Yearling
Dec
14
awarded  Nice Answer
Nov
22
comment Triangulation of the Klein Bottle
I disagree, but we may be talking about two different things. When he says edge 12 is shared by 4 triangles I think that means he's identifying all four edges of the square. I'm only identifying the top/bottom edges with themselves and the left/right edges with themselves. I see now this isn't explicit in the OP's picture, but it makes the answer correct and it's what I assume he meant.
Sep
24
answered If $G$ is a group with $|G|=2m$ and $m$ odd, then $G$ has exactly one element of order two
Sep
8
revised Semidirect product structure of Dihedral group
added 83 characters in body
Sep
8
revised Semidirect product structure of Dihedral group
added 83 characters in body
Sep
8
answered Semidirect product structure of Dihedral group
Sep
8
comment Semidirect product structure of Dihedral group
What is $p$? Is it $2$?
Sep
8
comment Equal on an open subset implies equal on the whole space?
@darijgrinberg: That should be an answer.
Sep
4
revised About group actions
added 17 characters in body
Sep
4
comment About group actions
Yea, I wrote the second paragraph before they posted that link, I agree that order is probably not what they're talking about.
Sep
4
answered About group actions
Sep
4
answered How did they derive the image from kernel?
Sep
4
comment Is this basic fact about prime pairs obvious?
@lulu: The question is about the relationship between the sets $A_p$ and $A_q$ when $p, q$ is a pair of prime numbers. That's what the "prime pair" in the title refers to.
Sep
4
answered Is this basic fact about prime pairs obvious?
Sep
3
comment Alternate proof of Cantor-Bernstein Theorem
Hint for the first part: Note that $\mathcal L$ is a set whose elemements are subsets of $E$. So you need to pick a subset of $E$ and try to prove that this subset $C$ satisfies the condition $g(F \setminus f(C)) \subseteq E \setminus C$. There are two obvious subsets of $E$ that you might try first, $E$ itself and the empty set $\emptyset$. One of those will work.
Sep
3
answered A question about injective modules
Sep
3
revised A more formal but intuitive understanding (on a definition) of a group action
added 934 characters in body
Sep
3
answered A more formal but intuitive understanding (on a definition) of a group action
Sep
3
revised A question about covariant functor
edited body