1. Baumslag, G., Gersten, S.M., Shapiro, M., Short, H.: Automatic groups and amalgams. (in preparation)
2. Borel, A., Harder, G.: Existence of discrete cocompact subgroups of reductive groups over local fields. J. Reine Angew. Math.298, 53?64 (1978)
3. Borel, A., Serre, J.-P.: Cohomologie d'immeubles et des groupesS-arithmetiques. Topology15, 211?232 (1976)
4. Brown, K.S.: Buildings. Berlin-Heidelberg-New York: Springer 1988
5. Bruhat, F., Tits, J.: Groupes r�ductifs sur un corps local I. Donn�es radicielles valu�es. Publ. Math. Inst. Hautes Etud. Sci.41, 5?251 (1972)