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