Play audio slide show -- Keyboard shortcut: 'x'  Back to slide -- Keyboard shortcut: 'u'        next -- Keyboard shortcut: 'n'  Annotated program -- Keyboard shortcut: 't'    Play sound for this slide -- Keyboard shortcut: 'y'  prog3.scm - The fac function.Slide 2 : 3
Program 1

;; Calculate the factorial of n.
;; .parameter n An integer
;; .pre-condition The integer must be non-negative.
;; .returns n!
(define (fac n)
  (if (= 0 n) 1 (* n (fac (- n 1)))))