(Appears as a regular paper in the proceedings of IEEE International Conference on Tools with Artificial Intelligence (ICTAI), IEEE Computer Society, Washington D.C. Nov. 2002, pp. 75-82.) Recent advances in constraint satisfaction and heuristic search have made it possible to solve classical planning problems significantly faster. There is an increasing amount of work on extending these advances to solving more expressive planning problems which contain metric time, quantifiers and resource quantities. One can broadly classify classical planners into two categories: (i) planners doing refinement search and (ii) planners iteratively processing a representation of finite size like a SAT encoding or planning graph or a constraint satisfaction problem (CSP). One key challenge in the development of planners casting planning as SAT or CSP is the identification of constraints which are satisfied if and only if there is a plan of steps. This task is even more complex for planners hand...