anchor.diff:              [];
           (Values) ->
               Values2 = merge_values(Values),
  -            orddict:erase(Module, Values2)
  +            lists:keydelete(Module, 2, Values2)
       end,
       riak_core_metadata:put({riak_kv, mutators}, list, Modifier, []).
   
  
positive.code: merge_values([], Acc) ->
      Acc;
  
  merge_values([Head | Tail], Acc) ->
      Acc2 = orddict:merge(fun merge_fun/3, Acc, Head),
      merge_values(Tail, Acc2).
  
  merge_fun(_Key, P1, P2) when P1 < P2 ->
      P1;
  merge_fun(_Key, _P1, P2) ->
      P2.
  
negative.code: register(Module, Priority) ->
      Modifier = fun
          (undefined) ->
              [{Priority, Module}];
          (Values) ->
              Values2 = merge_values(Values),
              insert_mutator(Module, Priority, Values2)
      end,
      riak_core_metadata:put({riak_kv, mutators}, list, Modifier).
  
  