How to check non registered user and display specified content

Hello, I am new to wordpress and find a problem when trying to display some part of a post/ page to non registered users only and hide it for all registered/ logged in users.

I get a fatal error message like this:

Fatal error: Call to undefined function is_user_logged_out() in /home4/username/public_html/xxxxxxxxxxx.com/wp-content/themes/wptheme/functions.php

My question is what is the opposite of is_user_logged_in() ?

Thanks