Definition same_except_cur (m m' : Mem.mem) :=
  Mem.mem_contents m = Mem.mem_contents m' /\
  max_access_at m = max_access_at m' /\
  Mem.nextblock m = Mem.nextblock m'.

Lemma predat_inj {phi loc R1 R2} : predat phi loc R1 -> predat phi loc R2 -> R1 = R2.