 In empirical testing and measurement in general relativity, the treatment of individual gravitating systems follows an analogous pattern. For the analysis of interactions within a local system, an asymptotically flat solution to Einstein’s equation plays a role analogous to the Newtonian system that approximates the conditions of Corollary VI. In general relativity, there can be non-negligible post-Newtonian effects, such as spatial curvature, and the non-linear superposition of gravitational fields. When they appear, empirical consequences such as anomalous precessions and light-bending provide tests of general relativity and other relativistic gravitation theories. (See Will 2018, ch. 4, especially 4.1–4.3). Abstractly, we might wish to treat such a system as isolated within a region of space-time that “flattens out” at infinity. Practically, it suffices to consider a region in which, at a sufficient remove from a system of mutually gravitating masses, curvature becomes negligible in comparison with the curvature induced by those masses locally. In other words, analogously to the Newtonian case, it is not necessary that such a system be isolated from external influences. It suffices that external influences make a negligible difference to the actions of the masses among themselves, and to the resulting configuration of the system. In short, instead of providing an exact account of the global symmetries of space-time, the idea of an inertial frame still provides a crucial practical tool for the empirical study of actual physical interactions.