If we imagine the gravitational field … to be removed, there does not remain [an inertial space], but absolutely nothing, and also no "topological space." For the … [functions of the gravitational field] … structural properties of the manifold. [An inertial space is a gravitational field with constant space-time functions (i.e., ds^2 = dx^2+dy^2+dz^2-c^2dt^2).]
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