@SuppressWarnings("unchecked")
		public E previous() {
			if (nextIndex == 0) {
				throw new NoSuchElementException();
			}
			if(next != null) {
				lastReturned = next = next.previous;
			} else {
				lastReturned = next = tail.previous; // index > 0 => not tail is not head.
			}
			nextIndex--;
			checkForComodification();
			return (E) lastReturned.object;
		}