Module BAF := BA_Facts BA.
Include BAF.
(* Now, we prove the axioms about relativization. Again, this mostly involves packing and unpacking the canonTree type and pushing around mkCanon. *)
Definition rel (a x:t) : t.
case_eq (proj1_sig x); intros.
destruct b.
exact a.
exact (exist (fun t => canonicalTree t) (Leaf false) I).
refine (exist _ (relativ_tree (proj1_sig a) (proj1_sig x)) _).
apply relativ_almost_canon.
apply (proj2_sig a).
apply (proj2_sig x).
destruct x; simpl in *; subst; simpl in *; intuition.
Defined.

Lemma relativ_tree_empty : forall a x,
nonEmptyTree a -> nonEmptyTree x ->
nonEmptyTree (relativ_tree a x).