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