1. Buchanan, T.: Ovale und Kegelschnitte in der komplexen projektiven Ebene. Math.-Phys. Sem. ber.26, 244?260 (1979).
2. Buchanan, T., H�hl, H., L�wen, R.: topologische Ovale. Geom. Dedic.9, 401?424 (1980).
3. Groh, H.: 1-dimensional orbits in flat projective planes. Math. Z.122, 117?124 (1971).
4. L�wen, R.: Projectivities and the geometric structure of topological planes. In:Plaumann, P., Strambach, K.: (Eds.): Geometry?von Staudt's Point of View. Proc. Conf. BadWindsheim1980, pp. 339?372. Dordrecht-Boston-London: Reidel. 1980.
5. L�wen, R.: Equivariant embeddings of low dimensional symmetric planes. Mh. Math.91, 19?37 (1981).