proposition: Lemma castmxEsub m1 m2 n1 n2 (eq_mn : (m1 = m2) * (n1 = n2)) A : castmx eq_mn A = mxsub (cast_ord (esym eq_mn.1)) (cast_ord (esym eq_mn.2)) A.
proof: Proof. by rewrite mxsub_cast !esymK; case: eq_mn. 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)