def minimum(self, x=None):
        """
        @return: The minimum value in the subtree rooted at x.
        """
        if None == x:
            x = self.root
        while x.left != self.nil:
            x = x.left
        return x

        @return: The minimum value in the subtree rooted at x.
        
recipes/Python/576817_Red_black_tree/recipe-576817.py