Consider the following premises. p_7 -> p_18. p_18 <-> w. ~w. p <-> p_7. Can we infer ~p from them?
 From p_18 <-> w, ~w we can infer ~p_18. From p_7 -> p_18, ~p_18 we can infer ~p_7. From p <-> p_7 we can infer p -> p_7. Finally, from p -> p_7, ~p_7 we can infer ~p. Therefore, the answer is yes.