mtableAalign2.tex

\begin{array}{cccc}
\mathrm{Top} & 3 & \frac{{a}+1}{2}  & \overset{\frac{{a}+1}{2} }{{y}} \\
\mathrm{Bottom} & 3 & \frac{{a}+1}{2}  & \overset{\frac{{a}+1}{2} }{{y}} \\
\mathrm{Center} & 3 & \frac{{a}+1}{2}  & \overset{\frac{{a}+1}{2} }{{y}} \\
\mathrm{Baseline} & 3 & \frac{{a}+1}{2}  & \overset{\frac{{a}+1}{2} }{{y}} \\
\end{array}