Consider the following premises. r -> p_16. p_16 <-> u_3. u_3 or ~p_16. Can we infer ~(r -> u_3) from them? If possible, name the inference rules being used at each step.
 From p_16 <-> u_3 we can infer u_3 -> p_16 via biconditional elimination. From u_3 or ~p_16 we can infer p_16 -> u_3 via rewriting. From u_3 -> p_16, p_16 -> u_3 we can infer u_3 <-> p_16 via biconditional introduction. From u_3 <-> p_16 we can infer p_16 -> u_3 via biconditional elimination. Finally, from r -> p_16, p_16 -> u_3 we can infer r -> u_3 via transitivity, which contradicts ~(r -> u_3). Therefore, the answer is no.