It's a bit tougher when they're registered
and can maintain (relatively)
complex state, though. Many (most?) PALs are registered.
I still think it is easier to look at the circuit, understanding how it
works and recreating the equations...
(ha ha ha, I have a logic analyser, I can do anything up to 400MHz, la
la la, I'm the greatest hacker of the world, la la la) :oD