proposition: Lemma mulr_sign (b : bool) x : (-1) ^+ b * x = (if b then - x else x).
proof: Proof. by case: b; rewrite ?mulNr mul1r. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)