proposition: Lemma rowsub_cast m1 m2 n (eq_m : m1 = m2) (A : 'M_(m2, n)) : rowsub (cast_ord eq_m) A = castmx (esym eq_m, erefl) A.
proof: Proof. by case: _ / eq_m in A *; apply: (mxsub_eq_id (cast_ord_id _)). 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)