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: For all z, z is a janitor if and only if z is a server. For all z, z is a server if and only if z is a janitor.
For all z, if z were a janitor, then z is a server can be inferred via the universal biconditional elimination rule. For all z, if z were a server, then z is a janitor can be inferred via the universal biconditional elimination rule. For all z, if z were a server, then z is a janitor can be inferred via the universal biconditional elimination rule. For all z, if z were a janitor, then z is a server can be inferred via the universal biconditional elimination rule.