intros a; red in |- *.
intros a0 t1 t2 H; inversion H.
Qed.
Hint Resolve distinct_pbleaves_pbleaf : core.

(* A left has distinct leaves if its subtree has it *)
Theorem distinct_pbleaves_pbleft :
forall t, distinct_pbleaves t -> distinct_pbleaves (pbleft t).