Derek Parfit argued that there is no defendable criterion to differentiate between the duplicate and the original. That led him to the conclusion that the feel

Derek Parfit argued that there is no defendable criterion to differentiate between the duplicate and the original. That led him to the conclusion that the feeling of being a particular person is itself an illusion - just a side-effect of sequential brain events so to say. This is obviously quite a counter-intuitive proposition, but also quite hard to argue against without resorting to mere believes. I guess Parfit would have considered this AI project an (albeit miniscule) achievement of immortality.