fact: Variables (Aul : 'M[R]_(m1, n1)) (Aur : 'M[R]_(m1, n2)).
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq path) mathcomp(ssralg fintype perm poly mxpoly finfun tuple) mathcomp(matrix bigop zmodp polydiv) ssrcomplements dvdring