(defun gray (a b c d)
        (setf res ())
        (if (= a 1)
                (setf res (cons res (cons '1 ())))
                (setf res (cons res (cons '0 ()))))
        (if (or (and (eq a 0) (eq b 1)) (and (eq a 1) (eq b 0)))
                (setf res (cons res (cons '1 ())))
                (setf res (cons res (cons '0 ()))))
        (if (or (and (eq b 0) (eq c 1)) (and (eq b 1) (eq c 0)))
                (setf res (cons res (cons '1 ())))
                (setf res (cons res (cons '0 ()))))
        (if (or (and (eq c 0) (eq d 1)) (and (eq c 1) (eq d 0)))
                (setf res (cons res (cons '1 ())))
                (setf res (cons res (cons '0 ()))))
        (print (cdaaar res))
        (print (cdaar res))
        (print (cdar res))
        (print (cdr res))
)
(gray (read) (read) (read) (read))