Hierarchical Finite State Controllers for Generalized Planning
  Finite State Controllers (FSCs) are an effective way to represent sequential
plans compactly. By imposing appropriate conditions on transitions, FSCs can
also represent generalized plans that solve a range of planning problems from a
given domain. In this paper we introduce the concept of {\it hierarchical FSCs}
for planning by allowing controllers to call other controllers. We show that
hierarchical FSCs can represent generalized plans more compactly than
individual FSCs. Moreover, our call mechanism makes it possible to generate
hierarchical FSCs in a modular fashion, or even to apply recursion. We also
introduce a compilation that enables a classical planner to generate
hierarchical FSCs that solve challenging generalized planning problems. The
compilation takes as input a set of planning problems from a given domain and
outputs a single classical planning problem, whose solution corresponds to a
hierarchical FSC.
