Implement 2.1

util.scm

@@ -0,0 +1,13 @@
+(define (assert a b)
+  (cond ((equal? a b) (display "[ok]"))
+    (else
+      (display "[error] ")
+      (display a)
+      (display " != ")
+      (display b)))
+  (newline))
+
+(define (gcd a b)
+  (if (= b 0) (abs a) (gcd b (remainder a b))))
+
+;(assert (gcd 93 15) 3)