I mean 1 - x * y can be interpreted as !(x & y) in a straight forward manner and the NAND gate is universal, so you could certainly express any combinational lo

I mean 1 - x * y can be interpreted as !(x & y) in a straight forward manner and the NAND gate is universal, so you could certainly express any combinational logic. Obviously x and y can be time dependent functions and I think it would not be too hard to find a suitable equation for some kind of flip-flop and then you already got everything for building arbitrary finite state machines. I guess you could even introduce things like gate delays and more realistic impulse responses without too much trouble. There are certainly many other ways to model different aspects of digital logic and I have no idea what exactly Feynman needed and used.