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_9. q <-> w. u_1 <-> q_9. u_1 <-> w.
q -> w can be inferred via the biconditional elimination rule. u_1 -> q_9 can be inferred via the biconditional elimination rule. u_1 -> w can be inferred via the biconditional elimination rule. w -> q can be inferred via the biconditional elimination rule. q_9 -> u_1 can be inferred via the biconditional elimination rule. w -> u_1 can be inferred via the biconditional elimination rule. ~u_1 can be inferred via the biconditional elimination rule.