proposition: Lemma get_reducef f k (krf : k \in reducef f) (kf : k \in f): Some (reducef f).[krf] = f.[kf].
proof: Proof. by rewrite Some_fnd fnd_reducef in_fnd. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)