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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 bottom(self):
 """ The row index that marks the bottom extent of the vertical span of this cell. This is one greater than the index of the bottom-most row of the span, similar to how a slice of the cell's rows would be specified. """

        if self.vMerge is not None:
            tc_below = self._tc_below
            if tc_below is not None and tc_below.vMerge == ST_Merge.CONTINUE:
                return tc_below.bottom
        return self._tr_idx + 1