[Haskell-cafe] linear: instance Additive (Point f) ??

Hi café, I'm in the middle of responding to https://github.com/goldfirere/units/pull/45 and trying to learn the `linear` package, which I have yet to use. I have what may be a basic question: why is there an `instance Additive f => Additive (Point f)` (in the Affine module)? It would seem that the whole point of Point is that it is *not* Additive. We don't want to add Points! Could someone enlighten me? Thanks! Richard PS: Of course, this instance is directly hurting my use of the package. But it is hurting my understanding of the package, because it disagrees with the mental model I've built up of the definitions.