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: u_4 <-> u. q_1 -> u. u_4 -> q_1.
u_4 -> u can be inferred via the transitivity rule. u_4 -> u can be inferred via the biconditional elimination rule. u -> u_4 can be inferred via the biconditional elimination rule.