proposition: Lemma smulr_closedN : smulr_closed -> oppr_closed S.
proof: Proof. by case=> SN1 SM x Sx; rewrite -mulN1r SM. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)