mrogers writes "Today is Bill Gates' last day as a full-time employee of Microsoft. After 33 years at the company, the one-time richest man in the world will be retiring at 52 to spend more time guiding the charitable Bill and Melinda Gates Foundation. What would you buy him as a retirement gift?"
We warn the reader in advance that the proof presented here depends on a
clever but highly unmotivated trick.
-- Howard Anton, "Elementary Linear Algebra"