Definition freeable_blocks: list (block * BinInt.Z * BinInt.Z) -> mpred :=
  fold_right (fun (bb: block*BinInt.Z * BinInt.Z) a => 
                        match bb with (b,lo,hi) => 
                                          sepcon (VALspec_range (hi-lo) Share.top (b,lo)) a
                        end)
                    emp.

Lemma PTree_elements_remove: forall {A} (T: PTree.tree A) i e, In e (PTree.elements (PTree.remove i T)) -> In e (PTree.elements T) /\ fst e <> i.