code: public OrderingList<S> reverseDirections() {
          if (size() == 0) {
              return this;
          }
          OrderingList<S> reversedList = emptyList();
          for (int i=0; i<size(); i++) {
              reversedList = reversedList.concat(get(i).reverse());
          }
          return reversedList;
      }
docs: Returns this list with all orderings in reverse.