stant values of v less than 1 +t 0 2 , dr/dt <(-1 + €/2) [slope assumption in the transition region], and (iv) every curve beginning in the transition region with t^t 0 and having r ^(-1 + e/2) reaches / [convexity]. At any point along our geodesic with t^t 0 and i^l +t 0 2 , we must, by (i) and (ii), have f ^(-l+e/2), and so, by (iii), £^0. Thus, i>^l+/ 0 2 , once achieved, is maintained; while by hypothesis it is achieved. We conclude that r ^(-1 +e/2) along some final segment of our geodesic, whence, by (iv), our geodesic reaches/.We note, finally, that these cases exhaust the possibilities for null geodesies. Hence, all null geodesies reach /, completing the demonstration of weak asymptotic simplicity.We wish to thank Bob Wald for helpful discussions.By a space-time we mean a smooth connected four-Recently there has been growing interest in condensed-matter systems characterized by nonlinear wave equations which possess solitary-manifold with a smooth, time-oriented metric of Lo-] rentz signature. Structure of Spacetime (Cambridge Univ. Press, Cambridge, 1973). 4 This condition essentially ensures that the genera-(O-tors of / are shear-free, and that the physical Ricci tensor vanishes sufficiently quickly asymptotically. The operations of taking derivatives, and of raising and lowering indices, are those with respect to the conformally scaled metric g ab .