Before revision:  In our context, systematic generalization implies that a good model should perform well on all new combinations of future actions after being trained on all of them, but only on a limited set of their combinations. For models to generalize out-of-distribution to unseen action combinations , they should reason about the states and their dependency relation with the applied actions.
After revision:  In our context, systematic generalization implies that a good model should perform well on all new combinations of future actions after being trained on all of them, but only on a limited set of the possible regimes. For NNs to depict such out-of-distribution to unseen action combinations , they should reason about the states and their dependency relation with the applied actions.