public static <E> E getOnlyElement(Iterable<E> traversal, E defaultElement) {
   return getOnlyElement(traversal.iterator(), defaultElement);
 }
 public static void verifyElementOrder(
     Iterable<? extends Element> elements, String key, Order order, int expectedCount) {
   verifyElementOrder(elements.iterator(), key, order, expectedCount);
 }
 public static <E> E getOnlyElement(Iterable<E> traversal) {
   return getOnlyElement(traversal.iterator());
 }