<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def emit(signal, *args, **kwargs):
 """Emit a signal by serially calling each registered signal receiver for the `signal`. Note: The receiver must accept the *args and/or **kwargs that have been passed to it. There expected parameters are not dictated by mixbox. Args: signal: A signal identifier or name. *args: A variable-length argument list to pass to the receiver. **kwargs: Keyword-arguments to pass to the receiver. """

    if signal not in __receivers:
        return

    receivers = __live_receivers(signal)

    for func in receivers:
        func(*args, **kwargs)