anchor.diff:  
   %% @doc Generate an unique identifier for a vertex.
   v_str({Id, _}) ->
  -  erlang:integer_to_list(erlang:phash2(Id)).
  +    erlang:integer_to_list(erlang:phash2(Id)).
  
positive.code: %%      and V2.
  %%
  -spec directly_connected(digraph:graph(),
      digraph:vertex(), digraph:vertex()) -> boolean().
  
  directly_connected(G, V1, V2) ->
    case digraph:get_short_path(G, V1, V2) of
      [V1, V2] -> true;
      _        -> false
    end.
  
  to_dot(Graph) ->
      case digraph_utils:topsort(Graph) of
  
negative.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) ->
      case directly_connected(G, V1, V2) of
          false -> [];
          true ->
              lists:flatmap(fun(Ed) ->
                  case digraph:edge(G, Ed) of
                      {_, _, To, _}=E when To =:= V2 -> [E];
                      _ -> []
                  end
              end, digraph:out_edges(G, V1))
      end.
  
  %% @doc Are V1 and V2 linked directly?
  %%
  