proposition: Lemma eqmor_epi (phi psi : 'Mor(M, N)) : phi %= psi -> is_epi phi -> is_epi psi.
proof: Proof. move=> eqp phi_epi P kapa. by rewrite -(eqmor_ltrans (eqmorMr _ eqp)) => /phi_epi. 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