Definition  source j m (b2:block) (ofs2:Z) : option(block * Z) :=
   if plt 1%positive (Mem.nextblock m)
   then sourceN (Pos.pred (Mem.nextblock m)) j m b2 ofs2
   else None.

Lemma sourceNone_LOOR: forall j m1 b2 ofs2 (N: None = source j m1 b2 ofs2) m2 (Inj12: Mem.inject j m1 m2), loc_out_of_reach j m1 b2 ofs2.