Fixpoint reach'' (m:mem) (B:block -> bool) (L:list (block * Z)): block -> bool:=
  match L with
    nil => B
  | l::L => match l with
             (b',z) => match ZMap.get z (PMap.get b' (Mem.mem_contents m))
                       with Fragment (Vptr b off) q  n => fun bb => eq_block bb b &&
                                               Mem.perm_dec m b' z Cur Readable  &&
                                               reach'' m B L b'
                           | _ => fun bb => false
                       end
            end
  end.

Lemma reach_reach'' m B L b1 : reach m (fun b => B b=true) L b1 <-> reach'' m B L b1=true.