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62 votes
5 answers
10k views

Does "finitely presented" mean "always finitely presented"? (Answered: Yes!)

Precisely, if an R-module M has a finite presentation, and Rk → M is some unrelated surjection (k finite), is the kernel necessarily also finitely generated? Basically I want to believe I can ...
Andrew Critch's user avatar
9 votes
3 answers
1k views

Does "finitely presented" mean "always finitely presented", considered in general

I'm wondering about the question "If we have a finitely presented __, is it necessarily finitely presented with respect to any finite generating set for it?" I know this is true for groups and ...
Harry Altman's user avatar
  • 2,585
6 votes
1 answer
299 views

Can a compact object be a nontrivial self-retract?

Let $\mathcal C$ be a locally finitely-presentable category, and let $X$ be a finitely-presentable object of $\mathcal C$. Question: Can there exist a nontrivial idempotent on $X$ whose fixed points ...
Tim Campion's user avatar
  • 63.9k
4 votes
0 answers
319 views

Polynomial objects in any concrete category

EDIT: The original question had a trivial answer: it's just a coproduct. New question below New Question: As shown below, in the category of commutative unital rings, the coproduct of a ring $R$ with $...
Chetan Vuppulury's user avatar