<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_lower_supported(cls, previous_version):
 """ Return the lower supported protocol version. Beta versions are omitted. """

        try:
            version = next(v for v in sorted(ProtocolVersion.SUPPORTED_VERSIONS, reverse=True) if
                           v not in ProtocolVersion.BETA_VERSIONS and v < previous_version)
        except StopIteration:
            version = 0

        return version