code: public T set(int index, T element)
      {
          if (index == 0)
          {
              T previousElement = this.element1;
              this.element1 = element;
              return previousElement;
          }
          throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + this.size());
      }
docs: set is implemented purely to allow the List to be sorted, not because this List should be considered mutable.