anchor.diff:  %%      as adding the same vertex multiple times removes any
   %%      metadata (labels).
   %%
  --spec add_if_pid(digraph:graph(), pid()) -> ok.
  +-spec add_if_pid(digraph:graph(), lasp_vertex()) -> ok.
   add_if_pid(Dag, Pid) when is_pid(Pid) ->
      case digraph:vertex(Dag, Pid) of
         false -> digraph:add_vertex(Dag, Pid);
  
positive.code: %%      only the ones linking to V2.
  %%
  -spec get_direct_edges(digraph:graph(),
                         digraph:vertex(), digraph:vertex()) -> list(edge()).
  
  get_direct_edges(G, V1, V2) ->
      lists:flatmap(fun(Ed) ->
  
negative.code:     gen_server:call(?MODULE, {add_vertices, Vs}, infinity).
  
  %% @doc Check if linking the given vertices will form a loop.
  -spec will_form_cycle(list(lasp_vertex()), lasp_vertex()) -> boolean().
  will_form_cycle(Src, Dst) ->
      gen_server:call(?MODULE, {will_form_cycle, Src, Dst}, infinity).
  
  