Consider the following premises. u_3 <-> u_2. p_4 <-> u_3. p -> p_4. ~u_2. Can we infer p from them?
 From u_3 <-> u_2, ~u_2 we can infer ~u_3. From p_4 <-> u_3, ~u_3 we can infer ~p_4. Finally, from p -> p_4, ~p_4 we can infer ~p, which contradicts p. Therefore, the answer is no.