Consider the following premises. s -> q_2. ~t_1. q_2 -> t_1. Can we infer ~s or t_4 from them?
 From q_2 -> t_1, ~t_1 we can infer ~q_2. From s -> q_2, ~q_2 we can infer ~s. Finally, from ~s we can infer ~s or t_4. Therefore, the answer is yes.