Consider the following premises. r_4 -> w. ~q_21. p_21 <-> q_21. r_4. Can we infer ~w from them?
 From p_21 <-> q_21 we can infer p_21 -> q_21. Finally, from r_4 -> w, r_4 we can infer w, which contradicts ~w. Therefore, the answer is no.