diff -r 244df77507c2 -r 253d1ccb65de core_marking2/docdiff_test3.scala
--- a/core_marking2/docdiff_test3.scala	Sun Sep 15 12:57:59 2024 +0100
+++ b/core_marking2/docdiff_test3.scala	Mon Jul 21 16:38:07 2025 +0100
@@ -1,15 +1,17 @@
 
-import C2._
+def urbanmain() = {
+  import C2._
 
-val urban_list1 = List("a", "b", "b", "c", "d")
-val urban_list2 = List("d", "b", "d", "b", "d")
+  val urban_list1 = List("a", "b", "b", "c", "d")
+  val urban_list2 = List("d", "b", "d", "b", "d")
 
-assert(prod(urban_list1, urban_list2) == 7)
-assert(prod(urban_list1, urban_list1) == 7)
-assert(prod(urban_list2, urban_list2) == 13)
+  assert(prod(urban_list1, urban_list2) == 7)
+  assert(prod(urban_list1, urban_list1) == 7)
+  assert(prod(urban_list2, urban_list2) == 13)
 
 
-val urban_listA = List("a", "b", "b", "c", "d")
-val urban_listB = List("1", "2", "3", "4", "5")
+  val urban_listA = List("a", "b", "b", "c", "d")
+  val urban_listB = List("1", "2", "3", "4", "5")
 
-assert(prod(urban_listA, urban_listB) == 0)
+  assert(prod(urban_listA, urban_listB) == 0)
+}