We are happy to note and acknowledge the great deal of detailed help and understanding that we have received over the years from Gilberto Silva-Ortigoza, our co-author on many of the earlier papers on the present subject. Many others have contributed to our understanding of asymptotically-flat spacetimes. Prime among them are Roger Penrose, Andrzej Trautman, Jerzy Lewandowski, Pawel Nurowski, Paul Tod, Lionel Mason, Jörg Frauendiener and Helmut Friedrich. We thank them all. We also want to thank the Center for Gravitational Wave Astronomy at the University of Texas at Brownsville for hospitality during the last stage of this work.
This work is licensed under a Creative Commons License.