25 Aug
2012
25 Aug
'12
5:03 a.m.
Dear categorists, Is there a standard name for those presheaves X on a category C such that Xf is a bijection for any f in C? I have sometimes called them "biactions" since any such X (considered as, say, a left action of C) is paired with the obvious presheaf X' on C^op (a right action of C): X'f = (Xf)^-1. Of course, they correspond, as categories over C, to discrete bifibrations. I also know that the separable or decidable presheaves are those for which every Xf is injective. Claudio [For admin and other information see: http://www.mta.ca/~cat-dist/ ]