anchor.diff:  
   nextprev(S,OP,TK) ->
     Iter = lvl_iter(S,key_vals),
  -  check_np(OP,lvl_mv_iter(Iter,TK),Iter,TK).
  +  try
  +    check_np(OP,lvl_mv_iter(Iter,TK),Iter,TK)
  +  after
  +    lvl_close_iter(Iter)
  +  end.
   
   check_np(prev,invalid_iterator,Iter,TK) ->
     %% lvl_mv_iter/2 moved the iterator to the first record after TK: in
  
positive.code:     end,
    Iter.
  
  lvl_mv_iter(Iter,Where) ->
    case eleveldb:iterator_move(Iter,Where) of
      {ok,Key,Val}             -> {Key,Val};
  
negative.code: key_getter(S,Tab) ->
    Fun = fun(TK,Acc) -> [tk_key(TK)|Acc] end,
    Iter = lvl_iter(S,keys_only),
    try
      R = fold_loop(lvl_mv_iter(Iter,Tab),Tab,Iter,Fun,[]),
      lists:reverse(R)
    after
      lvl_close_iter(Iter)
    end.
  
  fold_loop(invalid_iterator,_,_,_,Acc) ->
    Acc;
  