Desert island column: The long story of a short theorem

If you are stuck on a desert island and want to while the hours away doing some passive idle reading, then you may be disappointed because what I have in mind is only four lines long - not enough to keep you busy until the proverbial cruise ship that will save you shows up on the horizon. If you prefer, however, to spend your time on more active endeavors, such as scribbling away mathematical formulae on the sand to explore the implications of your brief reading, then what I have may keep you busy for quite long time.