Fixpoint wf_btree_over t :=
match t with BNode keys children =>
(length keys = 2 * d + 1)%nat /\
(children = [] \/ length children = S (length keys) /\ Forall wf_btree_aux children)
end.

Lemma find_leaf_path : forall v t p (Hfind : find_leaf v t = Some p)
(Hwf : wf_btree t),
leaf_path t (removelast p).