question.md

Up to now we have assumed that the plans we create always make sure that an action’s preconditions are satisfied. Let us now investigate what propositional successor-state axioms such as ${HaveArrow}^{t+1} {;;{\Leftrightarrow};;}{}$ $({HaveArrow}^t \land \lnot {Shoot}^t)$ have to say about actions whose preconditions are not satisfied.

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

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 achieve the goal?