Fiedler, A.: P.rex: An interactive proof explainer. This paper outlines the interactive proof explanation system P.rex , which adapts its explanation to the user and allows him anytime to utter questions or requests, to which it reacts flexibly. As a generic system, it can be connected to different theorem provers. The distribution is available via the P.rex home page at http://www.ags.uni-sb.de/ prex.