What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Mary is a nurse. For all x_12, x_12 is rich if and only if x_12 is poor. If John were poor, then Mary is not a nurse.
John is not poor. For all x_12, if x_12 were rich, then x_12 is poor. For all x_12, if x_12 were poor, then x_12 is rich.