proposition: Lemma class_class x: inc x (substrate r) -> classp r (class r x).
proof: Proof. move=> xs; move: (setQ_repi (inc_class_setQ xs)) =>/class_P rxr. by split =>//; [substr_tac | apply: class_eq1]. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)