Eventually, he decided to look at using “air logic“. Air logic uses pneumatic devices to create relays, limit switches, AND gates, NAND gates ... was to build a multiplexer whose elements ...

While it is true that you can build logic gates using ... NAND gate) and then the logic was all in how you wired them together. And in this context, the SPDT relay was used as a two input ...

We will install a NAND gate on the purple ... the value inverted by the NAND gate is output to the AND gate and then inverted. It can be arranged more simply by using the Invert circuit.