@Override
	public E set(int index, E element) {
		int i = indexOf(element);
		if(-1 == i) {
			return l.set(index, element);
		} else {
			Check.unsupportedoperation.fail();
			return null;
		}
	}
@ Override public E set ( int index , E element ) { int i = indexOf ( element ) ; if ( - 1 == i ) { return l . set ( index , element ) ; } else { Check . unsupportedoperation . fail ( ) ; return null ; } }
TODO