--- a/progs/pow.scala	Tue Oct 08 21:12:52 2019 +0100
+++ b/progs/pow.scala	Wed Oct 09 21:37:17 2019 +0100
@@ -6,6 +6,12 @@
   case n => concat(A, pow(A, n- 1))
 }
 
+val A = Set("1", "2", "3", "")
+val B = Set("1", "2", "3", "4", "5", "6", "")
+concat(A, B).size                     // -> 28 
+pow(B, 3).size 
+
+
 val A = Set("a", "b", "c", "d")
 pow(A, 4).size                            // -> 256