proposition: Lemma signrE (b : bool) : (-1) ^+ b = 1 - b.*2%:R :> R.
proof: Proof. by case: b; rewrite ?subr0 // opprD addNKr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)