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: w -> p_18. u_1. u -> p_12. p_18 <-> u. p_12 -> ~u_1.
~p_12 can be inferred via the modus tollens rule. u -> ~u_1 can be inferred via the transitivity rule. p_18 -> u can be inferred via the biconditional elimination rule. u -> p_18 can be inferred via the biconditional elimination rule.