What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all z, z is a musician if and only if z is a janitor. Sarah is a janitor if and only if Sarah is a musician.
If Sarah were a janitor, then Sarah is a musician. If Sarah were a musician, then Sarah is a janitor. For all z, if z were a musician, then z is a janitor. For all z, if z were a janitor, then z is a musician.