 What is known as Reiter’s solution to the frame problem assumes a so-called closed system, that is to say, a system in which all (relevant) actions and changeable properties (in this setting often called ‘fluents’ to emphasize their changeability over time) are known. By this assumption it is possible to express the (non)change as a consequence of performing actions as well as the issue of the check for the preconditions to ensure successful performance in a very succinct and elegant manner, and coin it in a so-called successor state axiom of the form