matrix{
ccol{ {roman "Top"} above {roman "Bottom"} above {roman "Center"} above {roman "Baseline"} }
ccol{ 3 above 3 above 3 above 3 }
ccol{ {{a + 1} over 2} above {{a + 1} over 2} above {{a + 1} over 2} above {{a + 1} over 2} }
ccol{ {y to {{a + 1} over 2}} above {y to {{a + 1} over 2}} above {y to {{a + 1} over 2}} above {y to {{a + 1} over 2}} }
}