anchor.diff:    ?SET(Id, tcp_state, established).
   
   %% --- listen ---
  +
  +listen_pre(S) ->
  +  length(S#state.sockets) < ?MAX_SOCKETS.
   
   listen_args(_) ->
     [port()].
  
positive.code:   end.
  
  %% --- deliver ---
  
  %% deliver_pre(S) ->
  %%   S#socket.rcvd /= S#socket.seq.
  
  deliver_sockets(S) ->
    [ Sock || Sock <- S#state.sockets,
  
negative.code: 
  %% --- open (connect) ---
  
  open_pre(S) ->
    length(S#state.sockets) < ?MAX_SOCKETS.
  
  open_args(_) ->
    [ip(), port()].
  
  