anchor.diff:          {ok,Val} -> {ok,Val}
       end.
   
  +-spec remove(Key,tree(Key,Val)) -> tree(Key,Val).
  +
   remove(Key,T = {ByVal,ByKey,Comp}) ->
       case dict:find(Key,ByKey) of
           error ->
  
positive.code: %% ===========================================================================================
  %% PRIVATE
  %% ===========================================================================================
  
  insert(Key,Val,{ByVal,ByKey,Comp}) ->
      ByKey1 = dict:store(Key,Val,ByKey),
  
negative.code:     end.
  
  add_key_to_val_idx(Key,Val,ByVal) ->
      Keys = gb_trees:get(Val,ByVal),
      Keys1 = gb_sets:add(Key,Keys),
      gb_trees:update(Val,Keys1, ByVal).
  