You can very easily evaluate a postfix expression with two (or even one) stacks using maybe a few dozen lines of code

You're just a bit clever, aren't you FF? I notice you also talked about AI (Artificial Intelligence) programming elsewhere. Have you ever tried getting computers to handle Natural Language or basic perceptual processing?

It's a bloody nightmare, and just fills you with awe as to the stuff that we human beings do without batting an eyelid.
Can't beat being given a new appreciation of life, and an enhanced sense of wonder. I sometimes think that's the greatest gift anybody can be given.

Fisk