Some theorems about omaps.
Theorem:
(defthm omap::lookup-of-update (equal (omap::lookup key (omap::update key1 val map)) (if (equal key key1) val (omap::lookup key map))))
Theorem:
(defthm omap::emptyp-of-keys-to-emptyp (equal (emptyp (omap::keys map)) (omap::emptyp map)))