anchor.diff:      Start = ["digraph dag {\n"],
       VertexList = digraph_utils:topsort(Graph),
       DrawedVertices =  lists:foldl(fun(V, Acc) ->
  -        Acc ++ v_str(V) ++ ";\n"
  +        Acc ++ v_str(V) ++ " [fontcolor=black, style=filled, fillcolor=\"#613B93\"];\n"
       end, Start, VertexList),
       unicode:characters_to_list(write_edges(Graph, VertexList, [], DrawedVertices) ++ "}\n").
   
  
positive.code:     {reply, ok, State};
  
  handle_call(to_dot, _From, #state{dag=Dag}=State) ->
      io:format(to_dot(Dag)),
      {reply, ok, State};
  
  handle_call({export_dot, Path}, _From, #state{dag=Dag}=State) ->
      R = file:write_file(Path, to_dot(Dag)),
  
negative.code: add_edges(Src, Dst, Pid) ->
      gen_server:call(?MODULE, {add_edges, Src, Dst, Pid}, infinity).
  
  %% @doc Return the dot representation as a string.
  -spec to_dot() -> {ok, string()}.
  to_dot() ->
    gen_server:call(?MODULE, to_dot, infinity).
  
  