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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _supported_rule(protocol, ethertype):
 """Checks that the rule is an IPv4 rule of a supported protocol"""

        if not protocol or protocol not in utils.SUPPORTED_SG_PROTOCOLS:
            return False

        if ethertype != n_const.IPv4:
            return False

        return True