proposition: Fact add_polyA : associative add_poly.
proof: Proof. by move=> p q r; apply/polyP=> i; rewrite !coef_add_poly addrA. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)