Consider the following premises. ~r_6. p_3 <-> q_14. p_3 -> r_6. u <-> q_14. Can we infer ~u from them? If possible, name the inference rules being used at each step.
 From p_3 <-> q_14 we can infer q_14 -> p_3 via biconditional elimination. From q_14 -> p_3, p_3 -> r_6 we can infer q_14 -> r_6 via transitivity. From q_14 -> r_6, ~r_6 we can infer ~q_14 via modus tollens. Finally, from u <-> q_14, ~q_14 we can infer ~u via biconditional elimination. Therefore, the answer is yes.