proposition: Lemma castmx_comp m1 n1 m2 n2 m3 n3 (eq_m1 : m1 = m2) (eq_n1 : n1 = n2) (eq_m2 : m2 = m3) (eq_n2 : n2 = n3) A : castmx (eq_m2, eq_n2) (castmx (eq_m1, eq_n1) A) = castmx (etrans eq_m1 eq_m2, etrans eq_n1 eq_n2) A.
proof: Proof. by case: m2 / eq_m1 eq_m2; case: m3 /; case: n2 / eq_n1 eq_n2; case: n3 /. 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)