proposition: Lemma zmod_closedD : zmod_closed -> addr_closed S.
proof: Proof. by case=> S0 SB; split=> // y z Sy Sz; rewrite -[z]opprK -[- z]sub0r !SB. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)