So would the barrier to making things like adders, latches, etc. (in other words, everything you need to build a Von Neumann computer) be that they don't have a

So would the barrier to making things like adders, latches, etc. (in other words, everything you need to build a Von Neumann computer) be that they don't have a way to make NOT gates? Or would making NOT gates out what they have not be a big deal?