Questions About Calling iRule from Another iRule

I have an iRule that works as intended when a user spams the F5 key, the iRule calls a proc with a static page. I want to now call a separate iRule that will bring up a CAPTCHA page. I have read the wiki about procs, but how would I make the iRule below "callable" ?

https://devcentral.f5.com/codeshare/google-recaptcha-challenge-irule