class Pair implements Serializable {

  @Override
  public boolean equals(Object obj) {
    if (this == obj) {
      return true;
    }
    if (obj == null) {
      return false;
    }
    if (getClass() != obj.getClass()) {
      return false;
    }
    Pair<?, ?> other = (Pair<?, ?>) obj;
    if (left == null) {
      if (other.left != null) {
        return false;
      }
    } else if (!left.equals(other.left)) {
      return false;
    }
    if (right == null) {
      if (other.right != null) {
        return false;
      }
    } else if (!right.equals(other.right)) {
      return false;
    }
    return true;
  }

  public  Pair(L l, R r);

}