What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: s_1 -> q_6. s_1 -> r_2. q_6 -> s_1.
q_6 -> r_2 can be inferred via the transitivity rule. s_1 <-> q_6 can be inferred via the biconditional introduction rule. q_6 <-> s_1 can be inferred via the biconditional introduction rule.