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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 set_allowed(self, initial_state, *allowed_states):
 # type: (str, *str) -> None """Add an allowed transition from initial_state to allowed_states"""

        allowed_states = list(allowed_states)
        self._allowed.setdefault(initial_state, set()).update(allowed_states)
        for state in allowed_states + [initial_state]:
            if state not in self.possible_states:
                self.possible_states.append(state)