G. W. Gibbons, S. N. Solodukhin; The Geometry of Small Causal Diamonds arXiv:hep-th/0703098 (Causal intervals)
The empire on which the sun never sets | causal theory of reference | Causal Structure | Causal dynamical triangulation | Ardeshir Irani on the sets of ''Alam Ara | Algebra of sets |