; I

(+ 128 256)
(* 65536 4096)
(+ 123 (* 456 789))
(/ (+ -1 (sqrt 5)) 2)
(sqrt (+ 2 (sqrt 3)))

; II

(define (foo x y)
   (sin (+ (* 2 x) (* 3 y))))

; III

(define (max x y z)
   (if (> x y)
       (if (> x z) x z)
       (if (> y z) y z)))


; IV
(define (mid x y z)
   (if (> x y)
       (if (> z x)
           x
           (if (< z y) y z))
       (if (> z y)
           y
           (if (< z x) x z))))
 

; V
(car (cdr (cdr (cdr xs))))

; VI
(define (yama x)
   (if (and (<= 0 x) (< x 1))
       x
       (if (and (<= 1 x) (<= x 2))
           (- 2 x))))

; VII
(define (circle g x y r)
   (graphics-operation g 'draw-ellipse (- x r) (- y r) (+ x r) (+ y r)))

; VIII
(define (butterfly g x1 y1 x2 y2)
   (graphics-draw-line g x1 y1 x1 y2)
   (graphics-draw-line g x1 y2 x2 y1)
   (graphics-draw-line g x2 y1 x2 y2)
   (graphics-draw-line g x2 y2 x1 y1))

; IX
(define (taiikuno-hi y)
  (let ((d (zeller y 10 1)))     ; day of Oct 1 (Oct 8) 
     (+ 8 (modulo (- 8 d) 7))))  ; 8+(8-d)%7

; X
(define (my-power x n)
   (if (= n 0)
       1
       (* x (my-power x (- n 1)))))