 The fifth \(\APUL\) reduction axiom is new. This axiom captures the essence of the action-priority update: for an agent to have defeasible knowledge after an action, she must have information about what happens as a result of more plausible actions and, further, she must have defeasible knowledge about the outcome of equi-plausible actions. The reason for this follows from the definition of the resulting plausibility relation \({\geq}[A]_a\). As a reminder, this is defined by setting \((v_1,f_1)\mathrel{{\geq}[A]_a}(v_2,f_2)\) if and only if we have one of the following: 