proposition: Fact oppmor_proof phi : pres N %| pres M *m (- phi%:m).
proof: Proof. by rewrite mulmxN dvdmxN dvdmx_morphism. Qed.
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