We investigate the face numbers of simplicial complexes with Buchsbaum vertex
links, especially pseudomanifolds with isolated singularities. This includes
deriving Dehn-Sommerville relations for pseudomanifolds with isolated
singularities and establishing lower bound theorems when the singularities are
also homologically isolated. We give formulas for the Hilbert function of a
generic Artinian reduction of the face ring when the singularities are
homologically isolated and for any pure two-dimensional complex.
The face ring of a simplicial complex modulo m generic linear forms is shown
to have finite local cohomology if and only if the link of every face of
dimension m or more is `nonsingular', i.e., has the homology of a wedge of
spheres of the expected dimension. This is derived from an enumerative result
for local cohomology of face rings modulo generic linear forms, as compared
with local cohomology of the face ring itself. The enumerative result is
generalized in slightly weaker form to squarefree modules.
A common generalization of two theorems on the face numbers of Cohen-Macaulay
(CM, for short) simplicial complexes is established: the first is the theorem
of Stanley (necessity) and Bjorner-Frankl-Stanley (sufficiency) that
characterizes all possible face numbers of a-balanced CM complexes, while the
second is the theorem of Novik (necessity) and Browder (sufficiency) that
characterizes the face numbers of CM subcomplexes of the join of the boundaries
of simplices.