The auxiliary verb is used with nothing following it, when confirming or contradicting a statement, in short answers to questions, or following comparatives. This pattern is used with the auxiliaries be, do, and have.
'I'm keeping my piranhas,' Paul said. 'No you're not,' said his mother. 'Yes I am,' said Paul.
'Is Debbie coming to see us tomorrow?' 'Yes, she is.'
'The governor never indicated during the campaign that he supported a gasoline tax.' 'No, he didn't.'
You'd imagine with age that I'd learn but I don't.
'You've never even seen it!' 'Yes I have,' snapped Betty.
My grandparents were very poor and they wanted their kids to do better than they had.