Consider the following premises. s_3 or ~q_18. s_3 <-> p_18. p_18 <-> q_18. Can we infer ~(p_18 <-> s_3) from them? If possible, name the inference rules being used at each step.
 From p_18 <-> q_18 we can infer p_18 -> q_18 via biconditional elimination. From s_3 <-> p_18 we can infer s_3 -> p_18 via biconditional elimination. From s_3 or ~q_18 we can infer q_18 -> s_3 via rewriting. From p_18 -> q_18, q_18 -> s_3 we can infer p_18 -> s_3 via transitivity. Finally, from p_18 -> s_3, s_3 -> p_18 we can infer p_18 <-> s_3 via biconditional introduction, which contradicts ~(p_18 <-> s_3). Therefore, the answer is no.