[Haskell-cafe] Type arithmetic with ATs

[Andrew Coppin]

OK, so I sat down today and tried this, but I can't figure out how.

There are various examples of type-level arithmetic around the place. 
For example,

http://www.haskell.org/haskellwiki/Type_arithmetic

(This is THE first hit on Google, by the way. Haskell is apparently THAT 
popular!) But this does type arithmetic using functional dependencies; 
what I'm trying to figure out is how to do that with associated types.

Any hints?

(I know for a fact that other people have done this - rule 34 requires it.)