code: @Override 
  	public boolean add(T e) {
  		if (elements instanceof List<?>) {
  			final List<T> l = (List<T>) elements;
  			int pos = Collections.binarySearch(l, e);
  			if (pos >= 0)
  				return false;
  			l.add(-(pos + 1), e);
  			return true;
  		}
  		return elements.add(e);
  	}
docs: {@inheritDoc}