proposition: Lemma invr_sign n : ((-1) ^- n) = (-1) ^+ n :> R.
proof: Proof. by rewrite -signr_odd; case: (odd n); rewrite (invr1, invrN1). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)