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: If William works, then Sarah is a doctor. Sarah is not a doctor. If it is overcast, then William is working. If Sarah were a doctor, then William is working.
William is not working can be inferred via the modus tollens rule. William is working if and only if Sarah is a doctor can be inferred via the biconditional introduction rule. Sarah is a doctor if and only if William is working can be inferred via the biconditional introduction rule.