code: function lessThan(xs, ys) {
      for (let i = 0; i < Math.min(xs.length, ys.length); i++) {
          if (xs[i] < ys[i])
              return true;
          if (xs[i] > ys[i])
              return false;
      }
      return xs.length < ys.length;
  }
docs: Compare two arrays by lexicographical order