Consider the following premises. p_8 <-> r_3. ~p_8. p -> r_3. u -> p. Can we infer ~u from them? If possible, name the inference rules being used at each step.
 From p_8 <-> r_3, ~p_8 we can infer ~r_3 via biconditional elimination. From u -> p, p -> r_3 we can infer u -> r_3 via transitivity. Finally, from u -> r_3, ~r_3 we can infer ~u via modus tollens. Therefore, the answer is yes.