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_4 -> t_4. s_4. q_17. t_4 -> s_4.
t_4 can be inferred via the modus ponens rule. s_4 and q_17 can be inferred via the conjunction rule. q_17 and s_4 can be inferred via the conjunction rule. s_4 <-> t_4 can be inferred via the biconditional introduction rule. t_4 <-> s_4 can be inferred via the biconditional introduction rule.