code: public static <T1 extends Comparable<T1>, T2 extends Comparable<T2>> int compare(T1 a1, T1 b1, T2 a2, T2 b2) {
          int res = N.compare(a1, b1);
  
          return res == 0 ? N.compare(a2, b2) : res;
      }
docs: Continue to compare the pairs of values <code>(a1, b1), (a2, b2)</code> until they're not equal.
  <code>0</code> is returned if all of the pairs of values are equal.
  
  @param a1
  @param b1
  @param a2
  @param b2
  @return