Is there any documentation on core.logic's protocols, or an example of how to extend it for a new, basically opaque type?

I'm just using the core.logic unifier in my tests in order to verify that two or three places in the structure have the same value, but I don't care what that value is.

Unfortunately, I've had to change that value from a string to a Datomic tempid, and that means the unifier breaks.

Because IUninitialized is not implemented on datomic.db.DbId.