via Steve Jurvetson – Stan Williams, HP guru, has figured out a way to implement all logic functions without negation. It is easy to implement all logic functions using only NAND or NOR gates, but not with just an AND or OR gate. He found the premise for this in a 160 year old philosophy book, and he calls the new gate IMP.
This allows him to implement all logic functions using only two-terminal devices (vs. three-terminal transistors traditionally used today).
Two-terminal devices are much easier to assembly on the nanoscale, using simple crossbars of metal, and/or self-assembly techniques.