anchor.diff:     bind(a, lists:last(Pids), A);
   
   bind(a, Pid, A) ->
  -   ioctl(Pid, {a, A});
  +   ioctl_(Pid, {a, A});
   bind(b, Pid, B) ->
  -   ioctl(Pid, {b, B}).
  +   ioctl_(Pid, {b, B}).
   
   %%
   %% make pipeline by binding stages
  
positive.code:   ,monitor/1
    ,demonitor/1
    ,ioctl/2
  
    % pipe i/o interface
    ,call/2
  
negative.code:    bind(a, lists:last(Pids));
  
  bind(a, Pid) ->
     ioctl_(Pid, {a, self()});
  bind(b, Pid) ->
     ioctl_(Pid, {b, self()}).
  
  bind(a, Pids, A)
   when is_list(Pids) ->
  