The cd-index of fans and posets
The number of flags in a complete fan, or more generally in an Eulerian poset, is encoded in the cd-index. We prove the non-negativity of the cd-index for complete fans, regular CW-spheres and Gorenstein* posets.(Published Online May 17 2006)
(Received May 18 2005)
(Accepted September 16 2005)
Key Words: cd-index; flag h-vector; Gorenstein* posets.
14M25 (primary); 06A07 (secondary).