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 -> q_3. u_1 -> q. q_3 -> u_1. q -> u_1.
q -> u_1 can be inferred via the transitivity rule. u_1 -> q_3 can be inferred via the transitivity rule. q_3 -> q can be inferred via the transitivity rule. u_1 <-> q can be inferred via the biconditional introduction rule. q <-> u_1 can be inferred via the biconditional introduction rule.