proposition: Lemma remove_eq_o : forall m x y, E.eq x y -> find y (remove x m) = None.
proof: Proof. intros. rewrite eq_option_alt. intro e. rewrite <- find_mapsto_iff, remove_mapsto_iff; now intuition. Qed.
imports: Bool DecidableType DecidableTypeEx OrderedType Morphisms FMapInterface