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2h
comment Is it possible to delete undesired identifications in algebraic structures?
If all you want to do is to factorise morphisms as monomorphisms followed by epimorphisms, or something like that, then you can look at the cograph factorisation $X \to X + Y \to Y$. The second half is always a split epimorphism, and the first half is a monomorphism in many interesting cases, e.g. in pointed categories.
7h
answered Is it possible to delete undesired identifications in algebraic structures?
9h
awarded  Announcer
15h
comment Image is not a manifold when considered as a subset: how is this possible?
For instance, consider a self-intersecting regular curve.
23h
awarded  Nice Answer
1d
answered Categories with some but not all exponentials
2d
comment Full stop as mutiplication sign
To say nothing of the Europeans who use a comma for the decimal point...!
2d
comment Lifting a homotopy class $S^k\to X$ into a simplicial set $X$ which is not fibrant but satisfies some weaker horn filling condition
What is $S^k$? Do you mean $\partial \Delta^{k+1}$?
Aug
30
comment Existence of tensor product via category theory
That result is more or less irrelevant. What you need is an adjoint functor theorem.
Aug
30
comment How to recover multiplication of group elements from category of groups?
The question could equally well be asked of the Lawvere theory of groups: given the Lawvere theory of groups as an abstract Lawvere theory, is there a way to recognise $(x, y) \mapsto x y$?
Aug
28
comment Is there a notation for “Bounded Kleene star”?
You could write $V^{\le n}$, perhaps. But you should explain it if you do.
Aug
28
comment How to recover multiplication of group elements from category of groups?
I don't think it is possible to distinguish $1 \mapsto x y$ from $1 \mapsto y x$.
Aug
28
comment If $M$and $N$ are R- modules, then under what conditions $\operatorname{Hom}(M,N)$ the space of R-module morphisms from M to N, is projective?
Here's something that is true, which you might like to prove: $\mathrm{Hom} (M, N)$ is projective if M is finitely generated projective and N is projective.
Aug
28
comment I need the paper “ J. Zhang, A note on finite groups satisfying the permutizer condition, Sci. Bull. 31 (1986) 363–365”
You will probably have to go to a library and look in the archives.
Aug
28
comment I need the paper “ J. Zhang, A note on finite groups satisfying the permutizer condition, Sci. Bull. 31 (1986) 363–365”
Here is the MathReview. It appears to have been published in China.
Aug
28
comment generalized affine scheme
That diagram is very important. Since $\bar{R}$ is left exact, coequalisers in $\mathbf{FPAlg}_k^\mathrm{op}$ are sent to equalisers in $\mathbf{Set}$.
Aug
27
comment Simple question about closed immersions
Yes, that's right.
Aug
26
comment Is it true that $A \in A$?
Errors like these are often caused by using $\cdots$ (or $\vdots$) without thinking about what it really means.
Aug
26
awarded  Revival
Aug
26
comment What is the “internal language of a topos”?
Yes. Of course, Grothendieck toposes are elementary toposes too.