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_join_sub {phi1 phi2 loc R} : join_sub phi1 phi2 -> predat phi1 loc R -> predat phi2 loc R.