Pentagramma Mirificum and elliptic functions
  We give an exposition of fragments from Gauss [G] where he discovered, with the help of some work of Jacobi, a remarkable connection between Napier pentagons on the sphere and Poncelet pentagons on the plane.   As a corollary we find a parametrization in elliptic functions of the classical dilogarithm five-term relation. 
Vadim Schechtman
math.AG