Recognizer for neteval-ordering-or-null structures.
(neteval-ordering-or-null-p x) → *
Theorem: consp-when-neteval-ordering-or-null-p
(defthm consp-when-neteval-ordering-or-null-p (implies (neteval-ordering-or-null-p x) (consp x)) :rule-classes :compound-recognizer)