[math-fun] coffee-ordering logicians

(Sorry if this is old. Via Craig Swanson.) Six logicians have finished their dinner together. The waitress comes and asks, "Do you all want coffee?" The first logician answers, "I don't know." 2nd: "I don't know." 3rd: "I don't know." 4th: "I don't know." 5th: "I don't know." 6th: "Yes." --Steve