I wanted to write a small package implementing vector spaces, etc. A part of it is class Module v s where (*>) :: s->v->v defining the multiplication of a vector by a scalar: w = a*>v Now, as in many other circumstances, concrete vectors are based on concrete scalars, and I defined really: class Module v s | v->s . One typical instance of vectors is the orthodox functional construction instance Num s => Module (v->s) s where (s*>f) x = s * (f x) and such tests: u = 2.5 *> sin; res = u 3.14 pass without tears. But I wanted also that operators of the type (b->s) -> (b->s), for example: inver f = recip . f . recip be vectors. So: instance ...=> Module ((v->s)->(v->s)) s where (s*>op) f = s*>(op f) But GHCi yells that two instances in view of the functional dependency declared are in conflict. Since I believe that I do not really understand fundeps in Haskell, and this is not a GHC 'feature' only, I send this query to the haskell list. I don't see this conflict. I could remove the fundep, but then I have other (smaller, but a bit annoying) problems, so I want to keep it, if only for my own instruction. Good people, help, please. Why v [->s] cannot "coexist" in this context with ((v->s)->v) [->s] Of course all extensions, including overlapping instances are on. Jerzy Karczmarczuk Caen, France