The princess asks her student, how many mares does a man need in his life? The student says, 'There's this land of ponies, it take ten days to go from north to south and ten days to go from east to west, every twenty years a man comes and takes nine tenths of the mares back to his harem. And when the sun expands, the planet becomes uninhabitable and there are no mares left in the land, the first percent of that man's mare needs will have been satisfied.'
