proposition: Lemma mxOverP {S : {pred T}} {M : 'M[T]__} : reflect (forall i j, M i j \in S) (M \is a mxOver S).
proof: Proof. exact/'forall_forallP. Qed.
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)