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