= Successor-state axiom
{title2=$F_{t+1}\leftrightarrow\operatorname{Add}_F(t)\lor(F_t\land\neg\operatorname{Delete}_F(t))$}
A logical equivalence characterizing exactly when a <planning fluent> is true after one step. Here $\operatorname{Add}_F$ and $\operatorname{Delete}_F$ are disjunctions of selected actions with the respective effects, under a suitable action-conflict policy. The persistence term excludes spontaneous changes and captures the relevant <frame axiom>. An implication from add effects alone would not constrain all other state changes.
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