--- a/marking2/docdiff_test3.scala	Tue Nov 19 06:38:20 2019 +0000
+++ b/marking2/docdiff_test3.scala	Fri Nov 22 16:41:45 2019 +0000
@@ -7,3 +7,9 @@
 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")
+
+assert(prod(urban_listA, urban_listB) == 0)