 It is worth noting that this can be phrased in a way which makes no reference to superclasses: for any class relation \(R\), there is a class relation \(R'\) such that for any \(x\) there is \(x'\) with preimage under \(R'\) equal to the preimage of \(x\) under \(R\), and distinct elements of the field of \(R'\) have distinct preimages.