mtable: $\begin{array}{ccc}\text{a}& \text{b}& \text{c}\\ \text{d}& \text{e}& \text{f}\end{array}$

mtable: $\begin{array}{|ccc|}\hline \text{a}& \text{b}& \text{c}\\ \text{d}& \text{e}& \text{f}\\ \hline\end{array}$