wrong placement of "| LoopEvent". It should be placed in "step_one": step_one(self, ev: StartEvent | LoopEvent), and NOT in "step_two"! The "step_two" should be without the "| LoopEvent": step_two(self, ev: ProcessingEvent). Why can't you even copy the demo code correctly?! The whole code of Chapter 2 is messed up!
