The Purloined Letter The Purloined Letter "The Purloined Letter" is a short story by American author Edgar Allan Poe. It is the third of his three detective stories featuring the fictional C. Auguste Dupin, the other two being "The Murders in the Rue Morgue" and "The Mystery of Marie Rogêt". These stories are considered to be important early forerunners of the modern detective story. It first appeared in the literary annual "The Gift for 1845" (1844) and was soon reprinted in numerous journals and newspapers. The unnamed narrator is discussing with the famous Parisian amateur detective C. Auguste Dupin some of his most
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