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