diff -r 27119b4a8d0f -r 41fee9bd4150 progs/pow.scala
--- a/progs/pow.scala	Sun Oct 27 13:45:54 2019 +0000
+++ b/progs/pow.scala	Sun Oct 27 13:55:43 2019 +0000
@@ -6,9 +6,9 @@
   case n => concat(A, pow(A, n- 1))
 }
 
-val A = Set("aa", "aaa")
-val B = Set("aaa", "aa")
-concat(A, B).size                     // -> 28 
+val A = Set("aa", "a")
+val B = Set("aaa", "aaaa")
+concat(A, B).size                     // -> 3