I like this puzzle because it's the same train of thought as this old joke: Three logicians walk into a bar. The bartender asks "Do you each want a drink?" Th

I like this puzzle because it's the same train of thought as this old joke: Three logicians walk into a bar. The bartender asks "Do you each want a drink?" The first logician says "I don't know." The second says "I don't know." The third logician says "Yes!"