Consider the following premises. q_3 -> t. ~t. s_3 -> q_3. t -> s_3. Can we infer s_3 from them? If possible, name the inference rules being used at each step.
 From s_3 -> q_3, q_3 -> t we can infer s_3 -> t via transitivity. From t -> s_3, s_3 -> t we can infer t <-> s_3 via biconditional introduction. Finally, from t <-> s_3, ~t we can infer ~s_3 via biconditional elimination, which contradicts s_3. Therefore, the answer is no.