the very simplest approaches might involve applying standard optimal graph search algorithms to the pruned search tree generated by TALplanner) and extending the planner to handle incomplete knowledge and non-deterministic operators. Which of these many topics will be the next focus of our research has not yet been determined.

## Acknowledgements

This research is supported in part by the WITAS Project under **the Wallenberg Foundation.**

## References

Bacchus, F., & Kabanza, F. (2000). Using temporal logics to express search control knowledge for planning. Artificial Intelligence, 116**(1–2), 123–191.**
Doherty, P. (1994). Reasoning about action and change using **occlusion. In Cohn, A. G.**
(Ed.), Proceedings of the 11th European Conference on Artificial Intelligence (ECAI94)**, pp. 401–405. John Wiley and Sons. Available at** ftp://ftp.ida.liu.se/pub/labs/
kplab/people/patdo/ecai94.ps.gz.

Doherty, P., Gustafsson, J., Karlsson, L., & Kvarnstr¨om, J. (1998). TAL: Temporal Action Logics - language specification and tutorial. **Electronic Transactions on Artificial**
Intelligence, 2**(3–4), 273–306. Available at** http://www.ep.liu.se/ej/etai/1998/009/.

Doherty, P., & Kvarnstr¨om, J. (1999). TALplanner: An empirical investigation of a temporal logic-based forward chaining planner. In Dixon, C., & Fisher, M. (Eds.), **Proceedings of**
the 6th International Workshop on Temporal Representation and Reasoning**, pp. 47–** 54. IEEE Computer Society. Available at ftp://ftp.ida.liu.se/pub/labs/kplab/people/ patdo/time99-final.ps.gz.

Doherty, P., & Kvarnstr¨om, J. (2001). TALplanner: A temporal logic-based planner. AI
Magazine, 22**(3), 95–102.**
Fox, M., & Long, D. (2003). PDDL2.1: An extension to PDDL for expressing temporal planning domains. **Journal of Artificial Intelligence Research, this issue**.

Gustafsson, J., & Doherty, P. (1996). Embracing occlusion in specifying the indirect effects of actions. In Aiello, L. C., Doyle, J., & Shapiro, S. C. (Eds.), **Proceedings of the 5th** International Conference on Principles of Knowledge Representation and Reasoning (KR-96)**, pp. 87–98, San Francisco. Morgan Kaufmann Publishers. Available at** ftp:
//ftp.ida.liu.se/pub/labs/kplab/people/patdo/final-kr96.ps.gz.

Karlsson, L., & Gustafsson, J. (1999). Reasoning about concurrent interaction. **Journal of**
Logic and Computation, 9**(5), 623–650.**
Kibler, D., & Morris, P. (1981). Don't be stupid. In Hayes, P. J. (Ed.), **Proceedings of the**
7th International Joint Conference on Artificial Intelligence (IJCAI-81)**, pp. 345–347.**
Kvarnstr¨om, J., & Doherty, P. (2003). TALplanner project page. http://www.ida.liu.se/
∼patdo/aiicssite1/kplab/projects/talplanner/.

Kvarnstr¨om, J., & Doherty, P. (2000). TALplanner: A temporal logic based forward chaining planner. Annals of Mathematics and Artificial Intelligence, 30**, 119–169.**