I am afraid that something is wrong with my understanding of multi- param classes with dependencies. I tried to generalize one of my old packages for quantum *abstract* computations, where state vectors are defined as functional objects, whose codomain has some arithmetic. It is easy to see that you can define (f <+> g) = \x -> f x + g x etc. It should be possible to curry this further, so I defined class Vspace a v | v -> a where (<+>) :: v -> v -> v (*>) :: a -> v -> v -- etc. instance Vspace a a where (<+>) = (+) (*>) = (*) -- etc. No problem. instance (Vspace a v) => Vspace a (c->v) where f <+> g = \x -> f x <+> g x (a *> f) x = a *> (f x) -- ... GHCi answers Cannot unify the type-signature variable `v' with the type `c -> v' Expected type: c -> v Inferred type: v When using functional dependencies to combine Vspace a a, arising from the instance declaration at ./Qutils.hs:30 Vspace a (c -> v), arising from the instance declaration at ./Qutils.hs:38 When trying to generalise the type inferred for `<+>' Signature type: forall a c v. (Vspace a v) => (c -> v) -> (c -> v) -> c -> v Type to generalise: (c -> v) -> (c -> v) -> c -> v Do YOU understand this, folks? Muchas gracias. Jerzy Karczmarczuk