What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? John is climbing a mountain if and only if Richard is taking a plane. John is not climbing a mountain. It is snowing if and only if Richard is taking a plane.
If John climbs a mountain, then Richard is taking a plane. If it snows, then Richard is taking a plane. If Richard takes a plane, then John is climbing a mountain. If Richard takes a plane, then it is snowing. Richard is not taking a plane.