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1.  Show that the axioms predict that nothing will happen when an action
    is executed in a state where its preconditions are not satisfied.<br />

2.  Consider a plan $p$ that contains the actions required to achieve a
    goal but also includes illegal actions. Is it the case that
$$
initial state \land successor-state axioms \land
p {\models} goal ?
$$

3.  With first-order successor-state axioms in situation calculus, is it
    possible to prove that a plan containing illegal actions will
    achi