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_validblock: forall l m b ofs (EFF: FreelistEffect m l b ofs = true), Mem.valid_block m b.