Consider the following premises. p_11 or ~u_4. p_11 -> u_4. u_4 -> p_11. Can we infer ~(u_4 <-> p_11) from them? If possible, name the inference rules being used at each step.
 From p_11 -> u_4, u_4 -> p_11 we can infer p_11 <-> u_4 via biconditional introduction. From p_11 or ~u_4 we can infer u_4 -> p_11 via rewriting. From p_11 <-> u_4 we can infer p_11 -> u_4 via biconditional elimination. Finally, from u_4 -> p_11, p_11 -> u_4 we can infer u_4 <-> p_11 via biconditional introduction, which contradicts ~(u_4 <-> p_11). Therefore, the answer is no.