--- a/marking4/re_test2.scala	Wed Oct 30 12:47:10 2019 +0000
+++ b/marking4/re_test2.scala	Wed Oct 30 14:07:58 2019 +0000
@@ -1,3 +1,4 @@
+import CW9c._
 
 assert(der('a', ZERO | ONE) == (ZERO | ZERO))
 assert(der('a', (CHAR('a') | ONE) ~ CHAR('a')) == ALT((ONE | ZERO) ~ CHAR('a'), ONE))