anchor.diff:  lvl_open(Dir,Tab) ->
     File = filename:join(Dir,Tab),
     case eleveldb:open(File,[{create_if_missing,true}]) of
  -    {ok,Handle} -> #lvl{table = Tab,handle = Handle,file = File};
  +    {ok,Handle} -> #lvl{name = Tab,handle = Handle,file = File};
       {error,Err} -> throw({500,{open_error,Err}})
     end.
   
  
positive.code:          dir}).
  
  -record(lvl,
          {table,
           file,
           handle}).
  
  init(Env) ->
    BaseDir = proplists:get_value(table_dir,Env),
  
negative.code:   %%   using it for a lookup in Tab1
    %% - Once the next Key1 is found, it needs to be converted to
    %%   external format before saving in Tab2
    case lvl_get(Lvl2,Key2) of
      not_found -> via(Lvl1,[],Lvl2,Key2,false);
      Key1      -> via(Lvl1,mk_ekey(Key1),Lvl2,Key2,true)
    end.
  
  via(Lvl1,Key1,Lvl2,Key2,Retry) ->
    case nextprev(Lvl1,next,Key1) of
      end_of_table when Retry ->
        via(Lvl1,[],Lvl2,Key2,false);
      end_of_table ->
        throw({409,end_of_table});
      {NextKey,V} ->
        NextVal = unpack_val(V),
        ins_overwrite(Lvl2,Key2,NextKey),
        {[{NextKey,NextVal}]}
    end.
  
  