docs: public static <T1, T2> TwoDimensionalCounter<T1, T2> scale(TwoDimensionalCounter<T1, T2> c, double d) {
      TwoDimensionalCounter<T1, T2> result = new TwoDimensionalCounter<T1, T2>(c.getOuterMapFactory(), c.getInnerMapFactory());
      for (T1 key : c.firstKeySet()) {
        ClassicCounter<T2> ctr = c.getCounter(key);
        result.setCounter(key, scale(ctr, d));
      }
      return result;
    }