Consider the following premises. p_8 <-> s. p_1 -> p_8. q_4 -> p_1. Can we infer q_4 -> s from them?
 From p_8 <-> s we can infer p_8 -> s. From p_1 -> p_8, p_8 -> s we can infer p_1 -> s. Finally, from q_4 -> p_1, p_1 -> s we can infer q_4 -> s. Therefore, the answer is yes.