anchor.diff:    ?INC(Id, seq),
     ?RET(ok).
   
  -sent_syn_ack_callouts(S, [Id]) ->
  +send_syn_ack_callouts(S, [Id]) ->
     Sock = get_socket(S, Id),
     ?MATCH(Packet, ?APPLY(sent, [Id])),
     ?ASSERT(?MODULE, check_packet, [Packet, '_', Sock#socket.rseq, [ack, syn]]),
  
positive.code:   ?SET(NewId, rseq,   {RemoteSeq, 1}),
    ?SET(NewId, socket_type, accept),
    ?SET(NewId, parent, Id),
    ?APPLY(sent_syn_ack, [NewId]),
    ?SET(NewId, tcp_state, syn_rcvd).
  
  
  
negative.code:        , ?APPLY(sent_ack, [Id]) ]),
    ?SET(Id, tcp_state, established).
  
  %% --- listen (passive open) ---
  
  listen_pre(S) ->
    length(S#state.sockets) < ?MAX_SOCKETS.
  