proposition: Lemma scalpE p q : scalp p q = if lead_coef q \in GRing.unit then 0 else rscalp p q.
proof: Proof. by case: ifP; rewrite /scalp unlock redivp_def => ->. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop ssralg poly)