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 -> q_2. w_4 or p_3. p_3 -> u. u <-> w_4. q_2 -> r_1. u -> p.
p -> r_1 can be inferred via the transitivity rule. p_3 -> p can be inferred via the transitivity rule. u -> q_2 can be inferred via the transitivity rule. u -> w_4 can be inferred via the biconditional elimination rule. w_4 -> u can be inferred via the biconditional elimination rule.