proposition: Lemma invr1 : 1^-1 = 1 :> R.
proof: Proof. by rewrite -{2}(mulVr unitr1) mulr1. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)