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_2 -> w. p_3 -> u_1. w -> u_1. w -> u_2. u_2.
w can be inferred via the modus ponens rule. u_2 -> u_1 can be inferred via the transitivity rule. u_2 <-> w can be inferred via the biconditional introduction rule. w <-> u_2 can be inferred via the biconditional introduction rule.