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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 clean_up_tabs(self):
 """ Method remove state-tabs for those no state machine exists anymore. """

        tabs_to_close = []
        for state_identifier, tab_dict in list(self.tabs.items()):
            if tab_dict['sm_id'] not in self.model.state_machine_manager.state_machines:
                tabs_to_close.append(state_identifier)
        for state_identifier, tab_dict in list(self.closed_tabs.items()):
            if tab_dict['sm_id'] not in self.model.state_machine_manager.state_machines:
                tabs_to_close.append(state_identifier)
        for state_identifier in tabs_to_close:
            self.close_page(state_identifier, delete=True)