Segments: How to exclude users with a specific action?

Hi there,

I want to find out the conversion rate of registrations on my website. Therefore I want to exclude all already registered users. But how do I do that? Is it possible to create a segment and exclude users with a specific event? I already have defined an event “registration confirmed”. So it would be perfect if I could exclude those users.

As far as I understand the segment creation process it is only possible to include actions, pageviews etc but not to exclude. Am I missing something?

Thanks for your help in advance!