1. Woodhouse, N.M.J.: The differential and causal structures of space-time. J. Math. Phys. 14(4), 495–501 (1973)
2. Ehlers, J., Pirani, F.A.E., Schild, A.: The geometry of free fall and light propagation. In: O’Raifeartaigh, L. (ed.) General Relativity, Papers in Honour of J.L. Synge, pp. 63–84. Clarendon, Oxford (1972)
3. Kundt, W., Hoffmann, B.: Determination of gravitational standard time. In: Recent Developments in General Relativity, pp. 303–306. Pergamon, Elmsford (1962). A book dedicated to Leopold Infeld’s 60th birthday
4. Audretsch, J.: Riemannian structure of space-time as a consequence of quantum mechanics. Phys. Rev. D 27(12), 2872–2884 (1983)
5. Grandou, G., Rubin, J.L.: On the ingredients of the twin paradox. Int. J. Theor. Phys. 48, 101–114 (2009)