The Graphplan Planner 66 The nogood Table nogood table (denoted ∇ ) for planning graph up to layer k: array of k sets of sets of goal propositions inner set: one combination of propositions that cannot be achieved outer set: all combinations that cannot be achieved (at that layer) before searching for set g in P j : check whether g ∈∇ (j) when search for set g in P j has failed: add g to ∇ (j)