What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all y, if y were a janitor, then y is a taxi driver. There is at least one y for which if y were a taxi driver, then y is a janitor. For all y, if y were a janitor, then y is a taxi driver.
There is at least one y for which y is a taxi driver if and only if y is a janitor. There is at least one y for which y is a taxi driver if and only if y is a janitor. There is at least one y for which y is a janitor if and only if y is a taxi driver. There is at least one y for which y is a janitor if and only if y is a taxi driver.