13. Intro Exercises 2

1. Simplify, explain and correct errors if needed.

   • (and (< x 10) (> x 3) (< x 12))
   • (or (= 0 1) (< 15 8) (string=? "dog" "DOG"))
   • (not (= (+ 1 3 7 9) (+ 2 4 6 8)))
   • (boolean=? (or (boolean=? lunchtime? true) study-hall?) false)

2. What does this function do? Is there any possibility of an error.

(define (mystery? n)
  (or (= n 0)
      (< 15 (/ 100 n))))

3. Does writing the function above in a different way matter?

(define (mystery2? n)
  (or (< 15 (/ 100 n))
      (= n 0)))

4. (Challenge) The lucky-charm? : image -> boolean. Give true if the image matches pic:unicorn (you can pick this image) or an orange star (must work for every size orange star). Write some check-expects first!

    (check-expect (lucky-charm? (star 20 "solid" "orange"))
                  true)
    (check-expect (lucky-charm? (star 30 "solid" "orange"))
                  true)
    (check-expect (lucky-charm? pic:hacker)
                  false)
    (check-expect (lucky-charm? pic:unicorn)
                  true)