…by getting the joke in this xkcd comic: http://xkcd.com/599/.
Thank you, The Man Who Loved Only Numbers! Currently in my reading rotation–it’s the bigraphy of Hungarian mathematician Paul Erdös. He was an author of about a bazillion papers and proofs and was known for a few things in particular: 1, being a great collaborator, 2, the elegance of his thinking, and 3, his itinerant lifestyle–he traveled all the time and would often show up on the doorsteps of fellow mathematicians with the pronouncement, “My brain is open.” He’d stay long enough to work on a problem together and then move on to the next place/idea. I like that guy.
Oh, and the joke is basically that mathematicians play their own sort of “Six Degrees of Kevin Bacon” game with Erdös because of his prolific collaborative papers, using what’s referred to as an “Erdös Number”. Erdös himself has an Erdös Number of 0; immediate collaborators have an Erdös Number of 1; those who collaborated with those collaborators have an Erdös Number of 2, and so on. It’s been said that 90% of the world’s active mathematicians have an Erdös Number lower than 8.