Permission to post in a forum. How do I disallow all people in one usergroup except all people in another?

[Stuart Wright]

I want people in one usergroup to never be able to post in a specific forum unless they are a member of a different specific usergroup.
I.e. people with the Adblocking usergroup can't post in the classified forums unless they have the Patreon usergroup.
Is this possible? Because I'm struggling to figure out how to do it.
Thanks
Permission to post in a forum. How do I disallow all people in one usergroup except all people in another?

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