One day a big asteroid will hit Earth, big enough to kill all our computers, but not big enough to wipe out all of humanity. We'll want to get back to working computers as quickly as possible, so that we can again play a round of Tetris after we've tilled our fields. It seems like a good idea to have a Lisp interpreter; perhaps that's small enough to hand-assemble into a running program. We can then use that to rebuild C compilers, email, gopher and usenet. Hopefully this time we'll forget how we made Java and spam.