proposition: Lemma intr_sign (R : ringType) s : ((-1) ^+ s)%:~R = (-1) ^+ s :> R.
proof: Proof. exact: rmorph_sign. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)