These formulae are not sufficient to derive everything that is considered plausible. Indeed, fluents at different situations are only related if they are preconditions and effects of actions; if a fluent is not affected by an action, there is no way to deduce it did not change. For example, the formula above does not imply that formula_94 follows from formula_95, which is what one would expect (the door is not made locked by opening it). In order for inertia to hold, formulae called "frame axioms" are needed. These formulae specify all non-effects of actions: