Addendum to: Summary Information for Reasoning About Hierarchical Plans
  Hierarchically structured agent plans are important for efficient planning
and acting, and they also serve (among other things) to produce "richer"
classical plans, composed not just of a sequence of primitive actions, but also
"abstract" ones representing the supplied hierarchies. A crucial step for this
and other approaches is deriving precondition and effect "summaries" from a
given plan hierarchy. This paper provides mechanisms to do this for more
pragmatic and conventional hierarchies than in the past. To this end, we
formally define the notion of a precondition and an effect for a hierarchical
plan; we present data structures and algorithms for automatically deriving this
information; and we analyse the properties of the presented algorithms. We
conclude the paper by detailing how our algorithms may be used together with a
classical planner in order to obtain abstract plans.
