I have a question that concerns multi value dependency. The relation looks like this:

R(A,B) with A -->> B (A multi value determines B)

I've been told that this relation is in 4th normal form, but I don't really se how. I know that if the multi value dependency is trivial, then it doesn't violate the 4th normal form. But is this trivial? It would be trivial if it, for example, looked like this:

{A,B} -->> B

But the first dependency example shouldn't be trivial.

The other rule for 4th NF says that A in this case needs to be a super key of the relation, but it isn't. As far as I can tell, A isn't a super key, since {A,B} is needed to identify a tuple.

So the question is, why is this in 4th normal form? It seems to be violating both of the rules.