Arrays
\begin{array}{||c|r|l||} a + b \\[2em] a + b & c & d \\[2em] \hline a + b \end{array}	$$\begin{array}{cc}& a+b\\ & \\ & a+b& c& d& \\ & & & & \\ & a+b\end{array}$$
\begin{array}{c:c:c} a & b & c \\ \hline d & e & f \\ \hdashline g & h & i \end{array}	$$\begin{array}{ccc}a& b& c\\ d& e& f\\ g& h& i\end{array}$$