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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 close(self):
 """Stops all the actors running a system of process applications."""

        super(ActorModelRunner, self).close()
        unsubscribe(handler=self.forward_prompt, predicate=self.is_prompt)
        if self.shutdown_on_close:
            self.shutdown()