Gentleman detective He lives in Paris with his close friend, the anonymous narrator of the stories. Like the much later Lord Peter Wimsey (see below), Dupin is a bibliophile, and met his narrator friend while both were searching for "the same rare and very remarkable volume" in an obscure library. For hobbies, Dupin is "fond" of enigmas, conundrums, and hieroglyphics. Dupin also bears the French title "Chevalier", meaning that he is a knight in the Légion d'honneur. The classic British gentleman detective appears soon after Poe's Dupin. A gentleman amateur is the ultimate hero of "The Moonstone" (1868), a famous epistolary novel
Dupin cyclide of Dupin cyclides is invariant under the larger group of all Lie sphere transformations; any two Dupin cyclides are Lie-equivalent. They form (in some sense) the simplest class of Lie-invariant surfaces after the spheres, and are therefore particularly significant in Lie sphere geometry. The definition also means that a Dupin cyclide is the envelope of the one-parameter family of spheres tangent to three given mutually tangent spheres. It follows that it is tangent to infinitely many Soddy's hexlet configurations of spheres. A further special property of a cyclide is: An elliptic cyclide can be represented parametrically by the following formulas