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: w_1 or w_4. w_1 -> u_4. w_4 <-> u_4.
w_4 -> u_4 can be inferred via the biconditional elimination rule. u_4 -> w_4 can be inferred via the biconditional elimination rule.