Recursive definition of logtail.
Theorem:
(defthm logtail* (implies (logtail-guard pos i) (equal (logtail pos i) (cond ((equal pos 0) i) (t (logtail (1- pos) (logcdr i)))))) :rule-classes ((:definition :clique (logtail$inline) :controller-alist ((logtail$inline t t)))))