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: ~s. w -> s. w <-> s_1.
~w can be inferred via the modus tollens rule. w -> s_1 can be inferred via the biconditional elimination rule. s_1 -> w can be inferred via the biconditional elimination rule.