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 -> r_15. u -> p_15. u. p_15 -> t. p_4 -> ~r_15.
p_15 can be inferred via the modus ponens rule. u -> t can be inferred via the transitivity rule. p_15 -> r_15 can be inferred via the transitivity rule.