public ORMultiValueDictionary <TKey, TValue> Prune(UniqueAddress removedNode, UniqueAddress collapseInto) =>
 new ORMultiValueDictionary <TKey, TValue>(Underlying.Prune(removedNode, collapseInto), _withValueDeltas);
 public PNCounterDictionary <TKey> Prune(UniqueAddress removedNode, UniqueAddress collapseInto) =>
 new PNCounterDictionary <TKey>(_underlying.Prune(removedNode, collapseInto));
 public ORMultiDictionary<TKey, TValue> Prune(UniqueAddress removedNode, UniqueAddress collapseInto) => 
     new ORMultiDictionary<TKey, TValue>(_underlying.Prune(removedNode, collapseInto));