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_1 -> t. ~u_3. u_3 or u_1. t -> ~u_1.
r_1 -> ~u_1 can be inferred via the transitivity rule. u_1 can be inferred via the disjunctive syllogism rule.