proposition: Lemma rpred_divr x y : x \in S -> x \is a unit -> (y / x \in S) = (y \in S).
proof: Proof. by rewrite -rpredV -unitrV; apply: rpredMr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)