@Override
 protected Iterator<?> createOneElementIterator() {
   return new DelayedPrependIterator<Integer>( //
       new ConstantThunk<Integer>(1), //
       Thriterators.<Integer>empty());
 }
 @Override
 protected Iterator<?> createTwoElementsIterator() {
   return new DelayedPrependIterator<Integer>( //
       new ConstantThunk<Integer>(1), //
       Thriterators.from(10));
 }