[kfogel]

There are algorithms where I think "Sure, with enough time and attention given to the problem, I might have thought of that." And then there are algorithms where I think "Oh, wow. That came from another planet. I would never have come up with that myself."

This one is definitely in the latter category.

[Retr0id]

Agreed. Further, for most algorithms, I can read a high-level description of it and go "ohhh, I get it now", and go away and implement it myself without further information. HashLife is not one of those algorithms! While I grok the concept of it, I'm pretty lost on how I'd turn that into functional code. I'm sure I could figure it out with enough further reading, though.