I'm trying to make a table of formulae. I've tried a bunch of different approaches (including `\parbox`, `align`, `eqnarray`, etc.), but none of these satisfy all of the requirements:

* `\hline` (or something equivalent) can still be used.
* Vertical lines can be put between columns
* Every cell can contain a formula in `\displaystyle`
* Formulae are centered both horizontally and vertically.

Does anybody know an environment that does this?