fact: Variables (m n : nat) (A : 'M[R]_(m, n)) (B : 'M[S]_(m, n)).
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)