On Generating Robust Plans and Linear Execution Strategies in Planning Against Nature

Planning against nature is a recent concept describing planning and acting in environments in which nature can non-deterministically trigger exogenous events, where the agent has to consider that the state of the environment might change without its consent. Therefore, the agent has to make sure that it eventually achieves its goal (if possible) despite the acts of nature. In this paper, we leverage the recent concept of robust plans, which assumes that nature might act as an adversary, to design a method for generating linear execution strategies, which assume that nature acts randomly but fairly. In particular, we consider events that have to eventually occur and facts that even if deleted by events will be eventually reachieved by (other) events (because nature acts fairly). To improve the efficiency of both robust plan and linear execution strategy generation methods, we provide an approach allowing us to adopt delete-relaxed heuristics that are used in classical planning.