© 1998 by London Mathematical Society
© The London Mathematical Society
CohenMacaulay Complexes and Koszul Rings
Mathematics Department, City University Northampton Square, London EC1V 0HB
Received 15 March 1994.
Throughout this paper k denotes a fixed commutative ground ring. A CohenMacaulay complex is a finite simplicial complex satisfying a certain homological vanishing condition. These complexes have been the subject of much research; introductions can be found in, for example, Björner, Garsia and Stanley [6] or Budach, Graw, Meinel and Waack [7]. It is known (see, for example, Cibils [8], Gerstenhaber and Schack [10]) that there is a strong connection between the (co)homology of an arbitrary simplicial complex and that of its incidence algebra. We show how the CohenMacaulay property fits into this picture, establishing the following characterization.
A pure finite simplicial complex is CohenMacaulay over k if and only if the incidence algebra over k of its augmented face poset, graded in the obvious way by chain lengths, is a Koszul ring.