anchor.diff:  init([]) ->
       {ok, #state{dag=digraph:new([acyclic]),
                   process_map=dict:new(),
  +                optimized_map=dict:new(),
                   contraction_step=0}}.
   
   -spec handle_call(term(), {pid(), term()}, #state{}) ->
  
positive.code:                     read :: function(),
                      transform :: function(),
                      write :: function()}).
  
  -type lasp_vertex() :: id() | pid().
  
  
negative.code: %%      where ( . ) is defined as the usual composition operator.
  %%      The result of this operation is a new edge h = (v1, v3).
  %%
  -spec contract(digraph:graph(), contract_path()) -> ok.
  contract(G, VSeq) ->
      [First, Second | _] = VSeq,
      Last = lists:last(VSeq),
  