Consider the following premises. ~r or p. p_6 <-> u. p -> u. r or p_6. Can we infer ~u from them?
 From p_6 <-> u we can infer p_6 -> u. From r or p_6, ~r or p we can infer p_6 or p. Finally, from p_6 -> u, p -> u, p_6 or p we can infer u, which contradicts ~u. Therefore, the answer is no.