JDRucker writes: "According to Katherine Krumme, the giants of their respective worlds were not only best of friends, but "fanboys" of each other's work. This image from Spring of 1894 shows Samuel Clemens (aka Mark Twain) acting as a conduit with Nikola Tesla in the background."
egrep patterns are full regular expressions; it uses a fast deterministic
algorithm that sometimes needs exponential space.
-- unix manuals