Definition FreeEffect m lo hi (sp b:Values.block) (ofs:Z): bool :=
   if valid_block_dec m b
   then eq_block b sp && zle lo ofs && zlt ofs hi
   else false.

Lemma FreeEffectD: forall m lo hi sp b z (FREE:FreeEffect m lo hi sp b z = true), b = sp /\ Mem.valid_block m b /\ lo <= z /\ z < hi.