Cuius rei demonstrationem mirabilem sane detexi hanc marginis exiguitas non caperet. I have a truly marvelous demonstration of this proposition which this margin is too narrow to contain. This was Fermat at his most infuriating. His own words suggest that he was particularly pleased with this “truly marvelous” proof, but he had no intention of bothering to write out the detail of the argument, never mind publishing it.
