2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/34374We review recent results by the author, in collaboration with Erwann Delay, Olivier Lengard, and Rafe Mazzeo, on existence and properties of space-times with controlled asymptotic behavior at null infinity.to appear in the proceedings of the Elba Conference in memory of A.Lichnerowicz, June 2002General Relativity and Quantum Cosmologytext