proposition: Lemma signr_addb b1 b2 : (-1) ^+ (b1 (+) b2) = (-1) ^+ b1 * (-1) ^+ b2 :> R.
proof: Proof. by rewrite mulr_sign; case: b1 b2 => [] []; rewrite ?opprK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)