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 -> u. r_8 -> p. u -> r_8. p -> r_8.
t -> r_8 can be inferred via the transitivity rule. u -> p can be inferred via the transitivity rule. r_8 <-> p can be inferred via the biconditional introduction rule. p <-> r_8 can be inferred via the biconditional introduction rule.