#lang sicp

(define (square n) (* n n))

(define (expmod-aux base exp n acc)
  (define sqr (remainder (square base) n))
  (cond ((= 0 exp) acc)
        ((even? exp)
         (if (and (= sqr 1)
                  (not (= base 1))
                  (not (= base (- n 1))))
             0
             (expmod-aux sqr (/ exp 2) n acc)))
        (else (expmod-aux base (- exp 1) n (remainder (* acc base) n)))))

(define (expmod base exp n)
  (expmod-aux base exp n 1))

(define (miller-rabin-test n)
  (define (try-it a)
    (= (expmod a (- n 1) n) 1))
  (if (and (even? n) (not (= 2 n)))
      #f
      (try-it (+ 1 (random (- n 1))))))