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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 mark_as_executed(self, req: Request):
 """ Works together with 'mark_as_forwarded' and 'free' methods. It makes request to be removed if all replicas request was forwarded to freed it. """

        state = self[req.key]
        state.executed = True
        self._clean(state)