anchor.diff:  
   start(Func, Mod, Options) ->
       SpawnOpt = proplists:get_value(spawn_opt, Options, []),
  -    gen_server:Func({local, proc_name(Mod)}, ?MODULE, [Mod, Options], [{spawn_opt, SpawnOpt}]).
  +    gen_server:Func({local, proc_name(Mod)}, ?MODULE, [Mod, Options],
  +                    [{spawn_opt, SpawnOpt}]).
   
   cast(Mod, Msg) -> gen_server(cast, Mod, Msg).
   call(Mod, Msg) -> gen_server(call, Mod, Msg).
  
positive.code:     {stop, normal, ok, S}.
  
  %% @hidden
  handle_cast({add_history, _Item}, #state{history=undefined}=S) ->
      {noreply, S};
  handle_cast({add_history, Item}, S) ->
      {noreply, S#state{history = [Item| S#state.history]}};
  
negative.code: handle_call({delete, Func, Arity}, _From, S) ->
      NewExpects = delete_expect(S#state.mod, {Func, Arity}, S#state.expects),
      {reply, ok, S#state{expects = NewExpects}};
  handle_call(history, _From, S = #state{history = undefined}) ->
      {reply, [], S};
  handle_call(history, _From, S) ->
      {reply, lists:reverse(S#state.history), S};
  