COMMENT ⊗   VALID 00002 PAGES
C REC  PAGE   DESCRIPTION
C00001 00001
C00002 00002	 functions for computing with cyclic list structures
C00004 ENDMK
C⊗;
;;; functions for computing with cyclic list structures

(defun count (x) (car (count1 x nil)))

(defun count1 (x u) (if
			(atom x) (cons 1 u)
			(member x u) (cons 0 u)
			((lambda (w) (foo (car w) (count1 (cdr x) (cdr w))))
				(count1 (car x) (cons x u)))))

(defun foo (n u) (cons (+ n (car u)) (cdr u)))

(defun cycle1 (u v) (if (null (cdr u)) (rplacd u v) (cycle1 (cdr u) v)))

(defun cycle (u) (cycle1 u u))

((lambda (x) nil)(setq a (cycle '(a b c))))

(defun nodes1 (x u) (if (member x u)	u
			(atom x)	(cons x u)
			(nodes1 (cdr x) (nodes1 (car x) (cons x u)))))

(defun count2 (x) (length (nodes1 x nil)))