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: p_8 -> u. u -> p_8. ~p_8. u -> p_8.
~u can be inferred via the modus tollens rule. ~u can be inferred via the modus tollens rule. p_8 <-> u can be inferred via the biconditional introduction rule. p_8 <-> u can be inferred via the biconditional introduction rule. u <-> p_8 can be inferred via the biconditional introduction rule. u <-> p_8 can be inferred via the biconditional introduction rule.