proposition: Lemma concat_in : forall m1 m2 y, In y (concat m1 m2) <-> In y m1 \/ In y m2.
proof: Proof. intros m1 m2; functional induction (concat m1 m2); intros; try factornode _x _x0 _x1 _x2 _x3 as m1. - intuition_in. - intuition_in. - rewrite join_in, remove_min_in, e1; simpl; intuition. Qed.
imports: FunInd FMapInterface FMapList ZArith Int