code: public static <E, C extends Counter<E>> double L1Norm(C c) {
      double sumAbs = 0.0;
      for (E key : c.keySet()) {
        double count = c.getCount(key);
        if (count != 0.0) {
          sumAbs += Math.abs(count);
        }
      }
      return sumAbs;
    }
docs: Return the L1 norm of a counter. <i>Implementation note:</i> The method
  name favors legibility of the L over the convention of using lowercase
  names for methods.
  
  @param c
  The Counter
  @return Its length