The Tachypomp :

A young mathematician wants to marry the lovely Abscissa Surd, but her father says he must first prove himself worthy. Professor Surd will only allow the protagonist to marry his daughter if he can either accomplish perpetual motion or faster-than-light travel. “The Tachypomp” is a short story for the mathematically-minded. Though first published anonymously in 1874, science-fiction scholar Sam Moskowitz rediscovered and republished it—along with Mitchell’s other forgotten work—in 1973, thus restoring him to his rightful place in contemporary sci-fi discourse.