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: William is a doctor if and only if Karen is working. For all y_4, y_4 will not work. Sarah is a janitor and Michael is cooking.
Sarah is a janitor can be inferred via the simplification rule. Michael is cooking can be inferred via the simplification rule. If William were a doctor, then Karen is working can be inferred via the biconditional elimination rule. If Karen works, then William is a doctor can be inferred via the biconditional elimination rule.