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_9 <-> u_4. u. p_9 -> ~u.
~p_9 can be inferred via the modus tollens rule. p_9 -> u_4 can be inferred via the biconditional elimination rule. u_4 -> p_9 can be inferred via the biconditional elimination rule.