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_4 or ~s_3. w_3 <-> u_4. ~w_3.
s_3 -> u_4 can be inferred via the rewriting rule. w_3 -> u_4 can be inferred via the biconditional elimination rule. u_4 -> w_3 can be inferred via the biconditional elimination rule. ~u_4 can be inferred via the biconditional elimination rule.