Effaceable functor
In mathematics, an effaceable functor is an additive functor F between abelian categories C and D for which, for each object A in C, there exists a monomorphism u: A \to M, for some M, such that F(u) = 0. Similarly, a coeffaceable functor is one for which, for each A, there is an epimorphism into A that is killed by F.