proposition: Lemma is_scalar_mx_is_diag A : is_scalar_mx A -> is_diag_mx A.
proof: Proof. by move=> /is_scalar_mxP[a ->]; apply: scalar_mx_is_diag. 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)