proposition: Lemma sym_submod_closed : submod_closed symmetric.
proof: Proof. split=> [|c p q /issymP sp /issymP sq]; apply/issymP=> s. by rewrite msym0. by rewrite msymD msymZ sp sq. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finfun bigop finset binomial) mathcomp(order fingroup perm ssralg zmodp poly ssrint) mathcomp(matrix vector) mathcomp(bigenough) ssrcomplements freeg