Consider the following premises. p_8 -> w. p_8 <-> u_3. s_3 -> p_8. ~s_3. w -> s_3. Can we infer ~u_3 from them? If possible, name the inference rules being used at each step.
 From p_8 -> w, w -> s_3 we can infer p_8 -> s_3 via transitivity. From s_3 -> p_8, p_8 -> s_3 we can infer s_3 <-> p_8 via biconditional introduction. From s_3 <-> p_8, ~s_3 we can infer ~p_8 via biconditional elimination. Finally, from p_8 <-> u_3, ~p_8 we can infer ~u_3 via biconditional elimination. Therefore, the answer is yes.