proposition: Lemma size_Msign p n : size ((-1) ^+ n * p) = size p.
proof: Proof. by rewrite -signr_odd; case: (odd n); rewrite ?mul1r // mulN1r size_opp. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)