Consider the following premises. r_2 <-> s_2. r_2 <-> s_2. Can we infer ~(s_2 <-> r_2) from them? If possible, name the inference rules being used at each step.
 From r_2 <-> s_2 we can infer r_2 -> s_2 via biconditional elimination. From r_2 <-> s_2 we can infer s_2 -> r_2 via biconditional elimination. Finally, from s_2 -> r_2, r_2 -> s_2 we can infer s_2 <-> r_2 via biconditional introduction, which contradicts ~(s_2 <-> r_2). Therefore, the answer is no.