fact: Definition const_mx m n a : 'M[R]_(m, n) := \matrix[const_mx_key]_(i, j) a.
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)