proposition: Lemma row_diag_mx n (d : 'rV_n) i : row i (diag_mx d) = d 0 i *: delta_mx 0 i.
proof: Proof. by apply/rowP => j; rewrite !mxE eqxx eq_sym mulr_natr. 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)