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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 _check_zero_size(self):
        '''
        Checks for zero height or zero width blocks and flags the occurrence.

        Returns:
            True if the block is size 0.
        '''
        block_zero = self.end[0] <= self.start[0] or self.end[1] <= self.start[1]
        if block_zero:
            self.flag_change(self.flags, 'fatal', worksheet=self.worksheet,
                             message=self.FLAGS['0-size'])
        return block_zero