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 Jennifer were a mechanic, then Jennifer is an office clerk. If Sarah were a lawyer, then Richard is a nurse. Jennifer is not an office clerk. If Barbara reads a book, then Sarah is a lawyer. Jennifer is a mechanic if and only if Richard is a nurse.
Jennifer is not a mechanic can be inferred via the modus tollens rule. If Jennifer were a mechanic, then Richard is a nurse can be inferred via the biconditional elimination rule. If Richard were a nurse, then Jennifer is a mechanic can be inferred via the biconditional elimination rule.