```scheme (+ 1 2) ; = 3 (* 3 4) ; = 12 (/ 8 2) ; 4 (* (+ 2 3) 4) ; 20 (define x 10) (define y (+ x 5)) (define (square n)) (* n n)) (square 6) ; 36 (define (factorial n) (if (= n 0) 1 (* n (factorial (- n 1))) )) (factorial 5) ; 120 ```