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 -> p. p -> r. t_4. r -> ~t_4.
~r can be inferred via the modus tollens rule. p -> ~t_4 can be inferred via the transitivity rule. r <-> p can be inferred via the biconditional introduction rule. p <-> r can be inferred via the biconditional introduction rule.