Ordered Landmarks in Planning

@article{Hoffmann2004OrderedLI,
  title={Ordered Landmarks in Planning},
  author={J{\"o}rg Hoffmann and Julie Porteous and Laura Sebasti{\'a}},
  journal={ArXiv},
  year={2004},
  volume={abs/1107.0052}
}
Many known planning tasks have inherent constraints concerning the best order in which to achieve the goals. A number of research efiorts have been made to detect such constraints and to use them for guiding search, in the hope of speeding up the planning process. We go beyond the previous approaches by considering ordering constraints not only over the (top-level) goals, but also over the sub-goals that will necessarily arise during planning. Landmarks are facts that must be true at some… 
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