May I please ask how to prove:
$\models (\Box A \lor \Box B) \equiv (\Box (\Box A \lor \Box B))$ is true in any $K$-$\rho \tau$ model.
$K$-$\rho \tau$ model means a $K$-model which is reflexive and transitive. $K$ represents the basic modal logic system. So $K$-$\rho \tau$ is a normal modal logic system.
$\rho$ - reflexivity
$\tau$ - transitivity
Any hints will be appreciated. Thanks so much.