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: q_3 -> p_4. ~u_1. p_4 -> u_1. u_1 -> p_4. p_4 -> q_3.
~p_4 can be inferred via the modus tollens rule. q_3 -> u_1 can be inferred via the transitivity rule. u_1 -> q_3 can be inferred via the transitivity rule. q_3 <-> p_4 can be inferred via the biconditional introduction rule. p_4 <-> u_1 can be inferred via the biconditional introduction rule. u_1 <-> p_4 can be inferred via the biconditional introduction rule. p_4 <-> q_3 can be inferred via the biconditional introduction rule.