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: t_4. t_4 -> s. s -> t_4.
s can be inferred via the modus ponens rule. t_4 <-> s can be inferred via the biconditional introduction rule. s <-> t_4 can be inferred via the biconditional introduction rule.