Consider the following premises. p <-> r. w. p_7 -> ~w. r <-> p_7. Can we infer p from them?
 From p_7 -> ~w, w we can infer ~p_7. From r <-> p_7, ~p_7 we can infer ~r. Finally, from p <-> r, ~r we can infer ~p, which contradicts p. Therefore, the answer is no.