Consider the following premises. ~w. u_1. p_10 -> w. w -> p_10. Can we infer p_10 from them? If possible, name the inference rules being used at each step.
 From p_10 -> w, w -> p_10 we can infer p_10 <-> w via biconditional introduction. Finally, from p_10 <-> w, ~w we can infer ~p_10 via biconditional elimination, which contradicts p_10. Therefore, the answer is no.