proposition: Lemma right_epi (M N L : {fpmod R}) (phi : 'Mor(M,N)) (psi : 'Mor(N,L)) : is_epi (phi ** psi) -> is_epi psi.
proof: Proof. by move=> mepi K kapa /(eqmorMl phi); rewrite mulmor0 mulmorA => /mepi. 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