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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 demote(self, move: chess.Move) -> None: """Moves a variation one down in the list of variations."""

        variation = self[move]
        i = self.variations.index(variation)
        if i < len(self.variations) - 1:
            self.variations[i + 1], self.variations[i] = self.variations[i], self.variations[i + 1]