diff -r 3b2f76950473 -r 5fcad75ade92 progs/pow.scala
--- a/progs/pow.scala	Sun Oct 02 08:42:01 2022 +0100
+++ b/progs/pow.scala	Sun Oct 09 13:39:34 2022 +0100
@@ -3,16 +3,29 @@
 
 def pow(A: Set[String], n: Int) : Set[String] = n match {
   case 0 => Set("")
-  case n => concat(A, pow(A, n- 1))
+  case n => concat(A, pow(A, n - 1))
 }
 
+def powT(A: Set[String], n: Int, acc: Set[String] = Set("")) : Set[String] = 
+  n match {
+    case 0 => acc
+    case n => powT(A, n - 1, concat(acc, A))
+  }
+
+
 val A = Set("a", "b", "c", "d", "e")
 val B = Set("a", "b", "c", "d", "")
 pow(A, 4).size
 pow(B, 4).size
+powT(A, 4).size
+powT(B, 4).size
 
 
-val A = Set("aa", "a")
+val C = Set("a", "b")
+
+pow(C, 100).size
+powT(C, 100000)  
+
 val B = Set("aaa", "aaaa")
 concat(A, B).size                     // -> 3