proposition: Lemma equiv_cast m1 n1 m2 n2 m3 n3 (eqm : m2 = m3) (eqn : n2 = n3) (A : 'M[R]_(m1,n1)) (B : 'M[R]_(m2,n2)) : equivalent A (castmx (eqm,eqn) B) <-> equivalent A B.
proof: Proof. by split; case: m3 / eqm A; case: n3 / eqn B. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype fintype finfun ssrnat seq) mathcomp(choice ssralg poly polydiv mxpoly matrix bigop) mathcomp(mxalgebra perm fingroup tuple) mxstructure dvdring