docs: @SuppressWarnings( { "unchecked" })
    public static <K1, K2> TwoDimensionalCounter<K2, K1> reverseIndexOrder(TwoDimensionalCounter<K1, K2> cc) {
      // they typing on the outerMF is violated a bit, but it'll work....
      TwoDimensionalCounter<K2, K1> result = new TwoDimensionalCounter<K2, K1>((MapFactory) cc.outerMF,
          (MapFactory) cc.innerMF);
  
      for (K1 key1 : cc.firstKeySet()) {
        ClassicCounter<K2> c = cc.getCounter(key1);
        for (K2 key2 : c.keySet()) {
          double count = c.getCount(key2);
          result.setCount(key2, key1, count);
        }
      }
      return result;
    }