Consider the following premises. p_7 or ~w. u_2 -> w. p_7 -> u_2. Can we infer u_2 <-> p_7 from them? If possible, name the inference rules being used at each step.
 From p_7 or ~w we can infer w -> p_7 via rewriting. From u_2 -> w, w -> p_7 we can infer u_2 -> p_7 via transitivity. Finally, from u_2 -> p_7, p_7 -> u_2 we can infer u_2 <-> p_7 via biconditional introduction. Therefore, the answer is yes.