Consider the following premises. s -> q_6. u. q_6 -> s. s -> ~u. Can we infer ~q_6 from them? If possible, name the inference rules being used at each step.
 From s -> q_6, q_6 -> s we can infer s <-> q_6 via biconditional introduction. From s -> ~u, u we can infer ~s via modus tollens. Finally, from s <-> q_6, ~s we can infer ~q_6 via biconditional elimination. Therefore, the answer is yes.