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_12 -> t_3. p_12 or ~u. r -> p_18. p_18 <-> u.
u -> p_12 can be inferred via the rewriting rule. p_18 -> u can be inferred via the biconditional elimination rule. u -> p_18 can be inferred via the biconditional elimination rule.