-let _select_descendant s t = SELECT_DESCENDANT(s,t, Tree.unordered_set_of_set t)
-let _select_following s t = SELECT_FOLLOWING(s,t, Tree.unordered_set_of_set t)
+let _select_descendant s t = SELECT_DESCENDANT(s,t, Tree.tag_list_of_set t)
+let _select_following s t = SELECT_FOLLOWING(s,t, Tree.tag_list_of_set t)