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 janitor if and only if z will play squash. There is at least one z for which if z reads a book, then z is a janitor. For all z, z will play squash if and only if z will read a book.
For all z, if z were a janitor, then z is playing squash. For all z, if z plays squash, then z is reading a book. For all z, if z plays squash, then z is a janitor. For all z, if z reads a book, then z is playing squash.