CONTINUAL HTN PLANNING AND ACTING IN OPEN-ENDED DOMAINS - Considering Knowledge Acquisition Opportunities Topics: Autonomous Systems; Cognitive Robotics; Knowledge Representation and Reasoning; Planning and Scheduling; Task Planning and Execution In Proceedings of the 4th International Conference on Agents and Artificial Intelligence - Volume 2: ICAART, 16-25, 2012 , Vilamoura, Algarve, Portugal