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<div id="hiddden">

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.<br 