--- a/progs/pow.scala	Sun Sep 27 09:15:32 2020 +0100
+++ b/progs/pow.scala	Tue Sep 29 00:51:43 2020 +0100
@@ -62,3 +62,25 @@
 val B = Set("a", "b", "")
 pow(B, 4)
 pow(B, 4).size
+
+
+
+val SA = Set("a", "b", "c", "d")
+val SB = Set("0", "1", "2", "3", "4", "5", "6")
+
+concat(SA, SB).size
+
+
+val SA2 = Set("ab", "a", "c", "d")
+val SB2 = Set("bc", "c", "2", "3", "4", "5", "6")
+
+concat(SA2, SB2).size
+
+
+/*
+((a b) c) d
+a (b (c d))
+(a b) (c d)
+(a (b c)) d
+a ((b c) d)
+*/