diff -r 29fc780ca130 -r fa7f7144f2bb main_solution3/re.scala
--- a/main_solution3/re.scala	Tue Dec 07 01:35:00 2021 +0000
+++ b/main_solution3/re.scala	Tue Dec 07 23:17:51 2021 +0000
@@ -108,6 +108,7 @@
   case r => r
 }
 
+simp(ALT(ONE | CHAR('a'), CHAR('a') | ONE))
 
 // (4) Complete the two functions below; the first 
 // calculates the derivative w.r.t. a string; the second