anchor.diff:      lists:foreach(fun(V) -> digraph:add_vertex(G, V) end, Vertices),
       lists:foreach(
           fun({V1, V2}) ->
  -            digraph:add_edge(G, {V1,V2}, V1, V2, [])
  +            digraph_add_edge(G, {V1,V2}, V1, V2, [])
           end, combinations2(Vertices)),
       {neighbors_from_digraph(G), edges_from_digraph(G), Vertices}.
   
  
positive.code:         fun({V1, V2}) ->
              digraph:add_vertex(G, V1),
              digraph:add_vertex(G, V2),
              digraph:add_edge(G, {V1,V2}, V1, V2, [])
          end, UniqueEdges),
      R = graph_from_digraph(G),
      digraph:delete(G),
      R.
  
negative.code:         fun({V1, V2}) ->
              case random:uniform() < P of
                  true ->
                      digraph_add_edge(G, {V1,V2}, V1, V2, []);
                  false ->
                      ok
              end
  