1. Beem, J.K., Ehrlich, P.E., Easley, K.L.: Global Lorentzian Geometry. Monographs and Textbooks in Pure and Applied Mathematics, vol. 202, 2nd edn. Marcel Dekker Inc., New York (1996)
2. Bernal, A.N., Sánchez, M.: Globally hyperbolic spacetimes can be defined as ‘causal’ instead of ‘strongly causal’. Class. Quantum Gravity 24(3), 745–749 (2007)
3. Bernard, P., Suhr, S.: Lyapounov functions of closed cone fields: from conley theory to time functions. Commun. Math. Phys. 359(2), 467–498 (2018)
4. Bredon, G.E.: Topology and Geometry. Graduate Texts in Mathematics, vol. 139. Springer, New York (1997)
5. Brickell, F., Clark, R.S.: Differentiable Manifolds: An Introduction. The New University Mathematics Series. Van Nostrand Reinhold, London (1970)