Proving the Temporal Properties of the Unique World Zoltán Horváth (1) Peter Achten (2) Tamás Kozsik (1) Rinus Plasmeijer (2) (1) Department of General Computer Science University Eötvös Loránd, Budapest, Hungary email: hz@ludens.elte.hu, tamas.kozsik@elte.hu (2) Faculty of Mathematics and Computer Science University Nijmegen, The Netherlands email: peter88@cs.kun.nl, rinus@cs.kun.nl Abstract The behavior of concurrent and parallel programs can be specified in a functional style. We introduced a relational model for synthesizing abstract parallel imperative programs earlier. In this paper we investigate the applicability of the specification and verification tools of the model for proving temporal properties of concrete programs written in a pure functional language, in Concurrent Clean. Destructive updates preserving referential transparency are possible by using so called unique types. Clean programs perform I/O by accessing their unique environment. We present a methodology for proving safety and liveness properties of concurrent, interleaved Clean Object I/O processes and show examples for verification of simple Clean programs.