Acknowledgments

This research was motivated by the Dagstuhl workshop on robot navigation, Dec 7-12, 2003. We thank all other participants for a fruitful atmosphere and motivating discussions. We thank Hartmut Surmann, Joachim Hertzberg, Kai Lingemann, Kai Pervölz, Matthias Hennig, Erik Demaine, Shmuel Gal, Christian Icking, Elmar Langetepe, Lihong Ma for preceding joint research that laid the foundations for this work, and Matthias Hennig, Rolf Mertig, and Jan van der Veen for technical assistance.