code: @Override
      public int compareTo(final Pair<L, R> other) {
        return new CompareToBuilder().append(getLeft(), other.getLeft())
                .append(getRight(), other.getRight()).toComparison();
      }
docs: <p>Compares the pair based on the left element followed by the right element.
  The types must be {@code Comparable}.</p>
  
  @param other  the other pair, not null
  @return negative if this is less, zero if equal, positive if greater