Consider the following premises. ~s. p_4 -> q. q -> t_4. s <-> t_4. Can we infer ~p_4 from them?
 From s <-> t_4, ~s we can infer ~t_4. From q -> t_4, ~t_4 we can infer ~q. Finally, from p_4 -> q, ~q we can infer ~p_4. Therefore, the answer is yes.