The only 1-related worlds of b is b itself. To check K1 K2(p r) at b, we simply have to check K2 (p r) at b. The 2-related worlds of b are b and d. Both of these worlds satisfy p r, so K2 (p r), and hence K1 K2(p r), is true at b.
Back to Question. Next Question.
Correct Answer.
r) at b, we simply have to check K2 (p