proposition: Lemma rev_unitrP (x y : R^c) : y * x = 1 /\ x * y = 1 -> x \is a unit.
proof: Proof. by case=> [yx1 xy1]; apply/unitrP; exists y. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)