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 sad if and only if z is an astronaut. John is not sad. It is late.
John is not sad and it is late. It is late and John is not sad. For all z, if z were sad, then z is an astronaut. For all z, if z were an astronaut, then z is sad.