Consider the following premises. s -> q_4. q_4 -> ~t. t. q_4 -> s. Can we infer s from them?
 From q_4 -> s, s -> q_4 we can infer q_4 <-> s. From q_4 <-> s we can infer s -> q_4. From q_4 -> ~t, t we can infer ~q_4. Finally, from s -> q_4, ~q_4 we can infer ~s, which contradicts s. Therefore, the answer is no.