diff -r 12d744ff9607 -r fd7f4f23d4af progs/pow.scala
--- a/progs/pow.scala	Tue Sep 29 19:35:11 2020 +0100
+++ b/progs/pow.scala	Tue Sep 29 21:52:52 2020 +0100
@@ -63,7 +63,9 @@
 pow(B, 4)
 pow(B, 4).size
 
-
+val C = Set("a", "")
+pow(C, 4)
+pow(C, 4).size
 
 val SA = Set("a", "b", "c", "d")
 val SB = Set("0", "1", "2", "3", "4", "5", "6")