public void add(E o) {
			checkForComodification();
			lastReturned = head;
			if(next == null) { // append to the end of the list
				if(append(o)) {
					expectedModCount++; 
				}
			} else {
				if(addBefore(o, next)) { // returns true if successfully inserted
					nextIndex++;
					expectedModCount++;
				}
			}
		}