proposition: Lemma vec_mx_delta m n i j : vec_mx (delta_mx 0 (mxvec_index i j)) = delta_mx i j :> 'M_(m, n).
proof: Proof. by apply/matrixP=> i' j'; rewrite !mxE /= [_ == _](inj_eq enum_rank_inj). Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype finfun bigop finset fingroup perm order) mathcomp(div prime binomial ssralg countalg finalg zmodp)