The fluent calculus is a formalism for expressing dynamical domains in first-order logic.
is used to concatenate the terms that represent facts that hold in a situation.
The frame problem is solved by asserting that the situation after the execution of an action is identical to the one before but for the conditions changed by the action.
For example, the action of moving the box from the table to the floor is formalized as: This formula states that the state after the move is added the term
is commutative and non-idempotent are necessary for such axioms to work.