proposition: Lemma modpN p q : (- p) %% q = - (p %% q).
proof: Proof. by apply/eqP; rewrite -addr_eq0 -modpD addNr mod0p. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop ssralg poly)