A “Tough Nuts” Track for the IPC

In the development of the IPC, there is an ongoing conflict between pushing the frontiers, and consolidating our technology. With growing PDDL, it becomes ever more difficult to achieve both. We propose to introduce a separate instrument for consolidation. A “tough nut” is a domain that can be addressed, language-wise, by existing planning techniques, but that cannot be solved efficiently. In a tough nuts track, domains would be submitted to the IPC committee, and a web repository of accepted domains and results would be maintained. A domain can be removed if it is considered “solved”. Awards can be given to the first technique that solves a domain, and to the domains that survive longest. This simple mechanism naturally keeps track of the challenges remaining behind the moving frontier of PDDL. It explicits open questions and encourages research on subtle issues.