Allow `><` syntax for product type?

[byorgey]

It's inconsistent that Cartesian product for sets requires >< (and disallows using *) but Cartesian product of types is the opposite. Perhaps we should just switch to requiring >< for both. Should wait until not in the middle of a semester to make this switch of course. It would also require updating a bunch of documentation.

[byorgey]

Note, the reason we can't allow * for Cartesian product of sets is that it would be very difficult to disambiguate/typecheck with * also meaning multiplication of numbers. There is no such issue with types.