Mehdi Vatandoost - Faculty of Mathematics and Computer Sciences, Hakim Sabzevari University, Sabzevar, Iran.

The causality ladder is well known as a classi cation of space-times by means ofcausal conditions in the Theory of Relativity. In this paper, we introduce a topological property of globally hyperbolic space-time which determines the difference of globally hyperbolic and causally simple space-time.

Space-time, Causality, Globally hyperbolic, Causally simple