Combine Parentpage and is_user_logged_in()

Is there any way to combine your ‘&global $post’ for parent pages and is_user_loged_in() ?

I tried:

&global $post; return (is_page('647') || ($post->post_parent=="647") & !is_user_logged_in());

But I’m getting an error because of the unexpected ‘&’. (Parse error: syntax error, unexpected ‘&’ in…)