C. Auguste Dupin features Dupin befriending a young boy named Edmund. The two solve mysteries together in Providence, Rhode Island. Dupin is revealed to be Edgar Allan Poe himself. Novelist George Egon Hatvary uses Dupin in his novel "The Murder of Edgar Allan Poe" (1997) as detective and narrator. Dupin travels to America to investigate the circumstances of Poe's mysterious death in 1849. In the novel, Dupin and Poe became friends when Poe stayed in Paris in 1829, and it was Poe who assisted Dupin in the three cases about which Poe wrote. Hatvary writes that Dupin resembles Poe, so much so that
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