Consider the following premises. q <-> s_4. q <-> q_13. p_17 -> ~t_2. t_2. ~q_13. Can we infer s_4 from them? If possible, name the inference rules being used at each step.
 From p_17 -> ~t_2, t_2 we can infer ~p_17 via modus tollens. From q <-> q_13, ~q_13 we can infer ~q via biconditional elimination. Finally, from q <-> s_4, ~q we can infer ~s_4 via biconditional elimination, which contradicts s_4. Therefore, the answer is no.