5 Acknowledgments

Most of this work was prepared while I was funded by a grant from DFG. I also benefitted from the MPI for Mathematics in the Sciences, Leipzig, where the article was completed. I wish to thank H. Friedrich for explaining some of the more subtle issues of null-infinity, and in particular of , to me. Thanks are also due to P. Hübner for providing me with some of the figures in Section 4.4. I also want to thank Ted Newman and Roger Penrose for filling me in on some of the historical developments of the subject. Finally, I want thank M. Hein and T. Vogel for carefully reading through the manuscript and checking the equations.

This work was prepared partly during the workshop “Gravitational interaction of compact objects” at the KITP in Santa Barbara. It was supported in part by the National Science Foundation under Grant No. PHY99-07949.