fact: Variables (Bh : 'M[R]_(m1, n1 + n2)) (Bv : 'M[R]_(m1 + m2, n1)).
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)