anchor.diff:  -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);
  -      _ -> ok
  +      false ->
  +           digraph:add_vertex(Dag, Pid);
  +      _ ->
  +           ok
      end;
   
   add_if_pid(_, _) ->
  
positive.code: v_str(V) when is_pid(V)->
      pid_to_list(V).
  
  depth(G, V, Max) ->
      case digraph:in_neighbours(G, V) of
          [] ->
              Max;
          Neighbors ->
              lists:foldl(fun(V1, MaxAcc) ->
                                  max(MaxAcc, depth(G, V1, Max + 1))
                          end, 0, Neighbors)
      end.
  
negative.code: 
  %% Defines how often an optimization pass happens.
  -define(CONTRACTION_INTERVAL, 1000).
  
  %% Initial depth of all nodes.
  -define(BASE_DEPTH, 0).
  
  %%%===================================================================
  %%% Type definitions
  