Consider the following premises. p_4 or ~w. w <-> p_4. Can we infer p_4 -> w from them? If possible, name the inference rules being used at each step.
 From p_4 or ~w we can infer w -> p_4 via rewriting. Finally, from w <-> p_4 we can infer p_4 -> w via biconditional elimination. Therefore, the answer is yes.