In the last years of his life von Neumann asked himself a question that sounded like philosophy: can a machine build a copy of itself? The difficulty is logical. To build a copy, the machine needs a description of itself; but the description is part of the machine, so it would have to describe itself, and so on, in an endless regress. Description, constructor and copier Von Neumann’s way out, presented in lectures from 1948 on, was to separate three pieces: