The University of Michigan Combinatorics Seminar


Abstract 

This talk will be about extensions of Rota's formula for the Möbius
function of a geometric lattice in terms of sets containing no broken
circuit (NBC sets). The extensions in question include one by Björner
describing the homology of a geometric lattice in terms of NBC sets,
another by Sagan and me extending Rota's formula to nongeometric
lattices, and another by Segev describing the homotopy type of the order
complex of a finite lattice. I'll present a more general and more
explicit version of Segev's result, which implies a Björnerlike
description of the homology of arbitrary finite lattices.
