--- a/progs/scala/re.scala	Wed Mar 04 19:34:47 2015 +0000
+++ b/progs/scala/re.scala	Mon Mar 09 10:49:17 2015 +0000
@@ -371,3 +371,12 @@
   time(lexing_simp(WHILE_REGS, prog2 * i))
 }
 
+val a0 = (EMPTY | "c") ~ ("b" | "cb")
+val a1 = der('c', a0)
+pretty(a1)
+val List(b1,b2,b3) = values(a1).toList
+vpretty(b1)
+vpretty(b3)
+vpretty(inj(a0,'c',b1))
+vpretty(inj(a0,'c',b3))
+