proposition: Lemma diag_mx_is_diag n (r : 'rV[V]_n) : is_diag_mx (diag_mx r).
proof: Proof. by apply/diag_mxP; exists r. 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)