proposition: Lemma divalg_closedZ : divalg_closed -> subalg_closed S.
proof: Proof. by case=> S1 Slin Sdiv; split=> //; have [] := @divr_closedM A S. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)