Authors: Yoav Segev, Peter Webb home page: http://www.math.umn.edu/~webb Address: School of Mathematics, University of Minnesota, Minneapolis MN 55455 Title: Extensions of G-posets and Quillen’s complex Abstract: We develop techniques to compute the homology of Quillen's complex of elementary abelian $p$-subgroups of a finite group in the case where the group has a normal subgroup of order divisible by $p$. The main result is a long exact sequence relating the homologies of these complexes for the whole group, the normal subgroup, and certain centralizer subgroups. The proof takes place at the level of partially-ordered sets. Notions of suspension and wedge product are considered in this context, which are analogous to the corresponding notions for topological spaces. We conclude with a formula for the generalized Steinberg module of a group with a normal subgroup, and give some examples. Subject Classification: Primary 20D30; Secondary 05E25, 06A09, 20C20, 51E25. Journal: J. Australian Math. Soc. (Series A) 57 (1994), 60-75.