Consider the following premises. ~u. p <-> s_3. u or ~s_3. Can we infer p from them? If possible, name the inference rules being used at each step.
 From u or ~s_3 we can infer s_3 -> u via rewriting. From s_3 -> u, ~u we can infer ~s_3 via modus tollens. Finally, from p <-> s_3, ~s_3 we can infer ~p via biconditional elimination, which contradicts p. Therefore, the answer is no.