Consider the following premises. p -> w. u -> p. u or ~w. Can we infer w <-> u from them? If possible, name the inference rules being used at each step.
 From u -> p, p -> w we can infer u -> w via transitivity. From u or ~w we can infer w -> u via rewriting. Finally, from w -> u, u -> w we can infer w <-> u via biconditional introduction. Therefore, the answer is yes.