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_2 -> s. t_2 <-> t_1. s <-> s_4. ~s_4.
t_2 -> t_1 can be inferred via the biconditional elimination rule. s -> s_4 can be inferred via the biconditional elimination rule. t_1 -> t_2 can be inferred via the biconditional elimination rule. s_4 -> s can be inferred via the biconditional elimination rule. ~s can be inferred via the biconditional elimination rule.