Definition FreelistEffect
  m (L: list (Values.block * Z * Z)) (b:Values.block) (ofs:Z): bool :=
  List.fold_right (fun X E b z => match X with (bb,lo,hi) =>
                                   E b z || FreeEffect m lo hi bb b z
                                 end)
                  EmptyEffect L b ofs.

Lemma FreelistEffect_same: forall m bb lo hi mm L (F:Mem.free m bb lo hi = Some mm) b (VB: Mem.valid_block mm b) ofs, FreelistEffect mm L b ofs = false <-> FreelistEffect m L b ofs = false.