proposition: Lemma restrict_mono (T : Type) (A B : {pred T}) (e : rel T) : {subset A <= B} -> subrel (restrict A e) (restrict B e).
proof: Proof. move => H x y /= => /andP [/andP [H1 H2] ->]. by rewrite !H. Qed.
imports: Coq(Setoid Morphisms) mathcomp(all_ssreflect) GraphTheory(edone)