fact: Structure mxsum_expr m n := Mxsum { mxsum_val :> wrapped 'M_(m, n); mxsum_rank : wrapped nat; _ : mxsum_spec (unwrap mxsum_val) (unwrap mxsum_rank) }.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype finfun bigop finset fingroup perm order) mathcomp(div prime binomial ssralg finalg zmodp matrix)