Probably true but some designs using transmission gates are so incredibly elegant. Look up Caldwell and Keister-Ritchie-Washburn and you will find that there are some classes of problems that are handled very nicely with transmission gates (AKA relays) but are cumbersome with more modern symbology. This class of problem is broadly called "iterative networks". And these are real world problems important to designers of low to high complexity systems in that era. Interestingly, since the modern tools no longer make these problems feasible, hardly anyone tries to solve them with the same efficiency anymore. (Some of the combinatoric problems that are easy with iterative networks happen to overlap closely with classic cryptography BTW.) Maybe, if you definition of pure digital design limits you to NANDS for example. But all the logic design handbooks/textbooks up until the 60's were inclusive of transmission gates as basic elements. Tim.