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