module ext_accessibility
  depends on accessibility

  axioms
    impossible occurs(X) if instance(X, actions),
                            agent(X, A),
                            instrument(X, I),
                            -accessible_to(I, A).

    impossible occurs(X) if instance(X, actions),
                            instrument(X, I),
                            -accessible(I).

    impossible occurs(X) if instance(X, actions),
                            agent(X, A),
                            object(X, O),
                            -accessible_to(O, A).