Re: knngist patch support

Dimitri Fontaine wrote:
> Then there's the metric space which is a data type with a distance
> function. This function must be non-negative, commutative, etc.
>
> So I guess what we need here is a Operator Group to define our plus and
> minus operators, and the fact that it's a group says (by convention,
> like the total ordering of a BTree) that the + is commutative and the -
> its opposite. Or we have an "option" called abelian for specifying the
> commutativity?
>   
Would the group analogy work with partially ordered domains, e.g. with a 
location on a sphere datatype together with an identifier for the sphere 
- so poi on earth can be compared to another, but not a poi on earth 
with a poi on the moon. ?

regards,
Yeb Havinga