fact: Definition coker : 'Mor(N, quot_by) := Morphism1 (dvd_quot_mx (dvdmx_refl _)).
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq path) mathcomp(ssralg fintype perm choice matrix bigop zmodp mxalgebra poly) ssrcomplements stronglydiscrete coherent edr