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 server if and only if z will sleep. For all z, if z sleeps, then z is a server. For all z, z is not a taxi driver. For all z, z is a taxi driver or z will not sleep.
For all z, if z sleeps, then z is a taxi driver can be inferred via the universal rewriting rule. For all z, if z were a server, then z is sleeping can be inferred via the universal biconditional elimination rule. For all z, if z sleeps, then z is a server can be inferred via the universal biconditional elimination rule.