Title Reasoning about Complex Actions with Incomplete Knowledge: a Modal Approach Authors Matteo Baldoni, Dipartimento di Informatica, Universita degli Studi di Torino Laura Giordano, Dipartimento di Scienze e Tecnologie Avanzate, Universita degli Studi del Piemonte Orientale Alberto Martelli, Dipartimento di Informatica, Universita degli Studi di Torino Viviana Patti, Dipartimento di Informatica, Universita degli Studi di Torino Main Fields 8. formal languages 19. theory of robotics 23. languages Other Main Fields reasoning about actions modal logic Abstract + Keywords In this paper we propose a modal approach for reasoning about dynamic domains in a logic programming setting. We present a logical framework for reasoning about actions in which modal inclusion axioms of the form \varphi \subset ... \varphi allows procedures to be defined for building complex actions from elementary actions. The language is able to handle knowledge producing actions as well as actions which remove information. Incomplete states are represented by means of epistemic operators and test actions can be used to check whether a fluent is true, false or undefined in a state. We give a non-monotonic solution for the frame problem by making use of persistency assumptions in the context of an  abductive characterization. A goal directed proof procedure is defined, which allows to reason about complex actions and to generate conditional plans.