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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 advancing(self):
 """A context manager for when time is moving forward one turn at a time. When used in LiSE, this means that the game is being simulated. It changes how the caching works, making it more efficient. """

        if self._forward:
            raise ValueError("Already advancing")
        self._forward = True
        yield
        self._forward = False