Consider the following premises. p or ~u_4. u_4 or ~p. Can we infer p <-> u_4 from them?
 From u_4 or ~p we can infer p -> u_4. From p or ~u_4 we can infer u_4 -> p. Finally, from p -> u_4, u_4 -> p we can infer p <-> u_4. Therefore, the answer is yes.