diff -r edb4ad356c56 -r 1dbf84ade62c progs/re4.scala
--- a/progs/re4.scala	Tue Oct 18 11:13:37 2016 +0100
+++ b/progs/re4.scala	Tue Oct 18 19:14:33 2016 +0100
@@ -30,8 +30,8 @@
     if (nullable(r1)) ALT(SEQ(der(c, r1), r2), der(c, r2))
     else SEQ(der(c, r1), r2)
   case STAR(r1) => SEQ(der(c, r1), STAR(r1))
-  case NTIMES(r, i) => 
-    if (i == 0) ZERO else SEQ(der(c, r), NTIMES(r, i - 1))
+  case NTIMES(r1, i) => 
+    if (i == 0) ZERO else der(c, SEQ(r1, NTIMES(r1, i - 1)))
 }
 
 def simp(r: Rexp) : Rexp = r match {
@@ -47,11 +47,6 @@
     case (r1s, ONE) => r1s
     case (r1s, r2s) => SEQ(r1s, r2s)
   }
-  case NTIMES(r1, n) => simp(r1) match {
-    case ZERO => ZERO
-    case ONE => ONE
-    case r1s => NTIMES(r1s, n)
-  }
   case r => r
 }