fact: Variables (A'ul : 'M[S]_(m1, n1)) (A'ur : 'M[S]_(m1, n2)).
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)