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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 register_observer(self):
 """ Register all observable which are of interest """

        self.execution_engine.add_observer(self, "start", notify_before_function=self.on_start)
        self.execution_engine.add_observer(self, "pause", notify_before_function=self.on_pause)
        self.execution_engine.add_observer(self, "stop", notify_before_function=self.on_stop)