Previous version replaced calls to, e.g., `cadr` with calls to `cdr`
then `car`, called the typechecker to populate the type table, then
optimized the exploded operations. The call to the typechecker failed
on open terms, limiting the applicability of the optimization, and was
just generally brittle.
The new version instead explodes operations, then optimizes them inside
out for as long as the argument's type guarantees it's safe. This works
on open terms, and should be more robust.
e997f02095