proposition: Lemma join_in : forall l x d r y, In y (join l x d r) <-> X.eq y x \/ In y l \/ In y r.
proof: Proof. join_tac. - simpl. rewrite add_in; intuition_in. - rewrite add_in; intuition_in. - rewrite bal_in, Hlr; clear Hlr Hrl; intuition_in. - rewrite bal_in, Hrl; clear Hlr Hrl; intuition_in. - apply create_in. Qed.
imports: FunInd FMapInterface FMapList ZArith Int