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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:
 async def on_isupport_casemapping(self, value):
 """ IRC case mapping for nickname and channel name comparisons. """

        if value in rfc1459.protocol.CASE_MAPPINGS:
            self._case_mapping = value
            self.channels = rfc1459.parsing.NormalizingDict(self.channels, case_mapping=value)
            self.users = rfc1459.parsing.NormalizingDict(self.users, case_mapping=value)