The expression \(\overline{X}^{i}_{jk}\gamma^{\,j}_{1}\gamma^{k}_{1}\) in equation (33) represents the inhomogeneous term of the transformation of the 4-acceleration. The inhomogeneity of the transformation law entails that a 4-acceleration that is zero with respect to one coordinate system is not zero with respect to another coordinate system. This means that there does not exist a unique standard of zero 4-acceleration that is intrinsic to the differential topological structure of spaceti