anchor.diff:  %%      and V2.
   %%
   -spec directly_connected(digraph:graph(),
  -    digraph:vertex(), digraph:vertex()) -> boolean().
  +                         digraph:vertex(), digraph:vertex()) -> boolean().
   
   directly_connected(G, V1, V2) ->
  -  case digraph:get_short_path(G, V1, V2) of
  -    [V1, V2] -> true;
  -    _        -> false
  -  end.
  +    case digraph:get_short_path(G, V1, V2) of
  +        [V1, V2] -> true;
  +        _        -> false
  +    end.
   
   to_dot(Graph) ->
       case digraph_utils:topsort(Graph) of
  
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) ->
    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?
  %%
  
negative.code: 
  %% @doc Generate an unique identifier for a vertex.
  v_str({Id, _}) ->
      erlang:integer_to_list(erlang:phash2(Id)).
  