iRule to Rewrite request and response

Hello I need help in coming up with an iRule for the below scenario.

http://mainapp.abc.com is the url for the main application.

http://about.mainapp.abc.com and http://contact.mainapp.abc.com are 2 diff sub applications.

The user will enter http://mainapp.abc.com/about or http://mainapp.abc.com/contact to access these sub applications.

So what I am looking for is -

User will enter - http://mainapp.abc.com/about The url should be rewritten to the back-end server as http://about.mainapp.abc.com when the page is returned to the client he should see http://mainapp.abc.com/about

How do I go about accomplishing this and thank you for your help and time.