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: r_4 -> ~s. s. t. ~r_4 -> q_1.
~r_4 can be inferred via the modus tollens rule. s and t can be inferred via the conjunction rule. t and s can be inferred via the conjunction rule.