anchor.diff:  %% @doc Remove
   %%------------------------------------------------------------------------------
   
  +%%------------------------------------------------------------------------------
  +%% @doc Update chain
  +%%------------------------------------------------------------------------------
  +
  +%%------------------------------------------------------------------------------
  +%% @doc Postorder
  +%%------------------------------------------------------------------------------
  +
  +%%------------------------------------------------------------------------------
  +%% Tests
  +%%------------------------------------------------------------------------------
   test_data_1() ->
     [{node, {"A", [], {i, [t], [[{t, 0}], [{t, 1}]]}},
       [{node, {"A", [{t, 1}], {i, [s], [[{s, 0}]]}},
  
positive.code: test_data_2() ->
    [{node, {"B", [], {i, [s], [[{s, 0}]]}},
      [{node, {"B", [{s, 0}], 1}, []}]}].
  
  test() ->
    lookup({"A",[]}, test_data_1()),
  
negative.code: 	  lookup({Xi,K0}, DTree)
        end;
      [] ->
        lookup({Xi,K0},DTree)
    end;
  lookup({Xi,K0}, [{node, {Xi,K1,V}, []}|DTree]) ->
    %%----------------------------------------------------------------------------
    %% If we reach a value in the DTree which is not an internal node, and not a
    %% {calc, W} value, we have reached a leaf node, so search the rest of the
    %% DTree.
    %%----------------------------------------------------------------------------
    lookup({Xi,K0}, DTree);
  lookup({Xi,K}, [{node, {Yi,_,_}, _}|DTree]) ->
    %%----------------------------------------------------------------------------
    %% When the Identifier is distinct, we are at the top level. Search the rest 
  