Some landmark factories provide an option to ensure that the returned landmark graph only contains causal landmarks (i.e., landmarks that either hold in the goal or make the relaxed planning task unsolvable when removing all actions satisfying the landmark in their precondition). This option is applied in the form of a post-processing step, removing all non-causal landmarks from the landmark graph. We have recently implemented similar post-processing steps (e.g., reasonable orderings) as a separate landmark factory instead of an option. It takes as an input the result of another landmark factory and outputs the processed (in this case filtered) landmark graph. On the command line call, this results in a nested set of landmark factories rather than adding a set of options. We would like to implement the post-processing for causal landmarks in this style as well.
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