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_2 <-> u_4. u_4 or q. w_2 <-> q.
w_2 -> u_4 can be inferred via the biconditional elimination rule. w_2 -> q can be inferred via the biconditional elimination rule. u_4 -> w_2 can be inferred via the biconditional elimination rule. q -> w_2 can be inferred via the biconditional elimination rule.