Skip to main content
2 of 7
addressed misread
Andrew Critch
  • 11.2k
  • 1
  • 50
  • 72

Does "finitely presented" mean "always finitely presented"?

Edit: I am not asking "does finite presentation imply coherent"...

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 choose generators for M however I please, and still get a finite presentation. I have reasons from algebraic geometry to believe this, but it seems like a very basic result, so I would like to understand it directly in terms of the commutative algebra, which I just can't seem to figure out...

(Here R is an arbitrary commutative ring, with no other hypotheses.)

Edit: All maps here are maps of R-modules. Also, the reason this is not the same as "does finite presentation imply coherent?" is that I am only asking for finite type kernels of surjections Rk → M.

Andrew Critch
  • 11.2k
  • 1
  • 50
  • 72