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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 flatten(self):
 """Internally flatten out nested iterables."""

    return PhaseGroup(
        setup=flatten_phases_and_groups(self.setup),
        main=flatten_phases_and_groups(self.main),
        teardown=flatten_phases_and_groups(self.teardown),
        name=self.name)