proposition: Lemma proj1_is_epi : is_epi proj1.
proof: Proof. move=> P phi; rewrite /eqmor !subr0 /=. by rewrite mul_col_mx mul0mx mul1mx dvd_mx_col => /andP[]. 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