condition, unit has skill?

Is there any such condition? In my map you buy all your skills from a shop, I want there be a way to sell your skills back though. So I thought of triggers like player types sell skill -impale remove impale and add the gold he paid for the item. However any player could type this just to get free gold, so I need a condtion like, unit has skill imaple.

Interger Comparison;
(Level of XSkill for (XUnit)) Greater than 0


I believe if that returns a Skill level of 0, then they can't have the spell. That should work, since anything 0 or less won't be accepted.