Question about calling a library from within a library

[eluser]neomech[/eluser]
I have extended the standard form_validation library to add a username check for Ion Auth. The following code works, but I'm wondering if I'm doing it right. In particular, I would have thought that I should be calling the ion_auth library from within the constructor, but doing that I was never able to get the line in the user_check function to recognize ion_auth. I'm not a PHP or CI guru by any means, but something about what I've done seems "wrong" to me....

Any comments on my approach here would be greatly appreciated!

Code:

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class MY_Form_validation extends CI_Form_validation {
      
    function My_Form_Validation()
    {
        parent::CI_Form_Validation();
    }
    
    function username_check($username)
    {
        $CI =& get_instance();
        $CI->load->library('ion_auth');
        return ($CI->ion_auth->username_check($username) ? FALSE : TRUE);
    }
}