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: u -> s. s -> r_6. p <-> r_6. ~p.
u -> r_6 can be inferred via the transitivity rule. p -> r_6 can be inferred via the biconditional elimination rule. r_6 -> p can be inferred via the biconditional elimination rule. ~r_6 can be inferred via the biconditional elimination rule.