What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? John is a nurse if and only if it is overcast. It is overcast if and only if John is a nurse.
If John were a nurse, then it is overcast. If it is overcast, then John is a nurse. If it is overcast, then John is a nurse. If John were a nurse, then it is overcast.