 Definition: A formula \(\varphi\) is said to be valid in the frame \(F=(W,R)\) iff every pointed Kripke model build on F satisfies \(\varphi\), i.e., iff for every \((M,w)=(F,V,w)=(W,R,V,w)\), \((M,w)\vDash\varphi\). A formula \(\varphi\) is valid on the class of frames \(\mathsf{F}\) (written \(\mathsf{F}\vDash\varphi\)) iff \(\varphi\) is valid in every frame F in \(\mathsf{F}\).