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 predat3 {phi loc R sh} : LK_at R sh loc phi -> predat phi loc (approx (level phi) R).