Recognizer for amb-declor/absdeclor structures.
(amb-declor/absdeclor-p x) → *
Theorem: consp-when-amb-declor/absdeclor-p
(defthm consp-when-amb-declor/absdeclor-p (implies (amb-declor/absdeclor-p x) (consp x)) :rule-classes :compound-recognizer)