Consider the following premises. q_13 -> r_6. p_13 <-> q_13. p_13 <-> r_6. Can we infer r_6 <-> p_13 from them? If possible, name the inference rules being used at each step.
 From p_13 <-> q_13 we can infer p_13 -> q_13 via biconditional elimination. From p_13 -> q_13, q_13 -> r_6 we can infer p_13 -> r_6 via transitivity. From p_13 <-> r_6 we can infer r_6 -> p_13 via biconditional elimination. Finally, from r_6 -> p_13, p_13 -> r_6 we can infer r_6 <-> p_13 via biconditional introduction. Therefore, the answer is yes.