This report describes an extension of planning graphs to handle conditional effects and true negation in the system IPP. Starting from the planning formalism ADL, a formal semantics for parallel plans containing actions with conditional effects is defined. We review the formalism of planning graphs, which was developed in the Graphplan system and show how the approach can be extended to deal with the full expressivity of ADL. In contrast to Graphplan, IPP does not generate the planning graph explicitely, but builds only one fact and action layer. Furthermore, actions and states are represetended using a bitvector representation, which allows for the time- and memory-efficient implementation of the sound and complete search algorithm. Technical Report No. 128 Contents 1 Technical Preliminaries 2 1.1 States, Planning Problems, Operators . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2 Conditional Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....