fact: Variables (Adl : 'M[aT]_(m2, n1)) (Adr : 'M[aT]_(m2, 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)