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 or q_4. q_4 -> q. ~s. s <-> u.
s -> u can be inferred via the biconditional elimination rule. u -> s can be inferred via the biconditional elimination rule. ~u can be inferred via the biconditional elimination rule.