Recursive definition of logext.
Theorem:
(defthm logext* (implies (logext-guard size i) (equal (logext size i) (cond ((equal size 1) (if (equal (logcar i) 0) 0 -1)) (t (logcons (logcar i) (logext (1- size) (logcdr i))))))) :rule-classes ((:definition :clique (logext) :controller-alist ((logext t t)))))