Consider the following premises. q <-> r. q_17. ~r. q <-> q_7. t -> ~q_17. Can we infer q_7 from them? If possible, name the inference rules being used at each step.
 From t -> ~q_17, q_17 we can infer ~t via modus tollens. From q <-> r, ~r we can infer ~q via biconditional elimination. Finally, from q <-> q_7, ~q we can infer ~q_7 via biconditional elimination, which contradicts q_7. Therefore, the answer is no.