Searching with probes: The classical planner probe. The 2011 International Planning Competition 30(29):71

Heuristic search has been the mainstream approach in plan-ning for more than a decade, with planners such as FF, FD, and LAMA being able to solve problems with hun-dreds of actions and variables in a few seconds (Hoff-mann and Nebel 2001; Helmert 2006; Richter and Westphal 2010). The basic idea behind these planners is to search for plans using a search algorithm guided by heuristic es-timators derived automatically from the problem (McDer-mott 1996; Bonet and Geffner 2001). State-of-the-art plan-ners, however, go well beyond this idea, adding a number of techniques that are specific to planning. These tech-niques, such as helpful actions and landmarks (Hoffmann and Nebel 2001; Hoffmann, Porteous, and Sebastia 2004; Richter, Helmert, and Westphal 2008), are designed to ex-ploit the propositional structure of planning problems;