He could respond that way to everyone.<p>In every full set of TAOCP, there is a sentence that reads &quot;If you have read this far, mail this string to the author to collect $25.&quot; The sentence is followed by a 10 character alphanumeric string. The string and placement of this sentence is randomized: different in every set.<p>To this day only 3 people have collected their checks. All three have them framed on their walls.