(set '0 nil)
(set '1+ (lambda (x) (cons t x)))
(set '1- (lambda (x) (cdr x)))

(set '1 (1+ 0))
(set '2 (1+ 1))
(set '3 (1+ 2))
(set '4 (1+ 3))
(set '5 (1+ 4))
(set '6 (1+ 5))
(set '7 (1+ 6))
(set '8 (1+ 7))
(set '9 (1+ 8))
(set '10 (1+ 9))

(set '& (lambda (x y) (if x (if y t))))
(set '| (lambda (x y) (if x t (if y t))))
(set '! (lambda (x) (if x nil t)))
(set 'xor (lambda (x y) (| (& x (! y)) (& (! x) y))))

(set '= (lambda (x y) (if (& x y) (= (1- x) (1- y)) (if (| x y) nil t))))
(set '< (lambda (x y) (if (& x y) (< (1- x) (1- y)) (if (| x y) (if x nil t)) nil)))
(set '<= (lambda (x y) (| (= x y) (< x y))))
(set '> (lambda (x y) (! (<= x y))))
(set '>= (lambda (x y) (| (= x y) (> x y))))
(set '+ (lambda (x y) (if y (1+ (+ x (1- y))) x)))
(set '- (lambda (x y) (if y (1- (- x (1- y))) x)))
(set '* (lambda (x y) (if y (+ (* x (1- y)) x) 0)))
(set '% (lambda (x y) (if (> x y) (% (- x y) y) (if (< x y) x 0))))
(set '/ (lambda (x y) (if (< x y) 0 (1+ (/ (- x y) y)))))
(set '^ (lambda (x y) (if y (* x (^ x (1- y))) 1)))
(set 'log (lambda (x y) (if (>= x y) (1+ (log (/ x y) y)) 0)))
(set 'gcd (lambda (x y) (if y (gcd y (% x y)) x)))
(set 'fib (lambda (x) (if (< x 2) x (+ (fib (- x 2)) (fib (- x 1))))))


(set 'append (lambda (x y) (if x (if y (cons (car x) (append (cdr x) y)) x) (if y y))))
(set 'reverse (lambda (x) (if x (append (reverse (cdr x)) (cons (car x) nil)) nil)))
(set 'length (lambda (x) (if x (1+ (length (cdr x))) 0)))

(set 'string->digit
     (lambda (x)
       (if (= x 9) '(9)
	 (if (= x 8) '(8)
	   (if (= x 7) '(7)
	     (if (= x 6) '(6)
	       (if (= x 5) '(5)
		 (if (= x 4) '(4)
		   (if (= x 3) '(3)
		     (if (= x 2) '(2)
		       (if (= x 1) '(1) '(0))))))))))))


(set 'digit->string
     (lambda (x)
       (if (equal x '9) 9
	 (if (equal x '8) 8
	   (if (equal x '7) 7
	     (if (equal x '6) 6
	       (if (equal x '5) 5
		 (if (equal x '4) 4
		   (if (equal x '3) 3
		     (if (equal x '2) 2
		       (if (equal x '1) 1 0)))))))))))

(set 'string->list
     (lambda (x) (if (> x 9)
		     (append (string->list (/ x 10)) (string->digit (% x 10)))
		   (string->digit x))))

(set 'list->string
     (lambda (x) (if (= (length x) 1) (digit->string (car x))
		   (+ (digit->string (car (reverse x)))
		      (* 10 (list->string (reverse (cdr (reverse x)))))))))

(set 'atom? (lambda (x) (equal x x)))
(set 'list? (lambda (x) (if x (! (atom? x)) t)))

(string->list (fib (+ 10 5)))