What is a set ?

[Mikal Ziane (Univ. Paris 5 and INRIA)]

Suppose I want to define the abstract data type SET.
How can I do that ?

Of course it depends what I want to do with it, but suppose I want the most
versatile definition which could give me a basis to define models in the future
(to build programs).
In other words is it reasonable to try and define SET as a (reusable) data
type ?

One question is set of what ?
If I don't want to define sets as subsets of some domain, but more
generally, am I doomed ? (because domains are set themselves ?)

Do I absolutely need a "member" operator.
If yes, and if I don't want sets to be just subsets, then I need a universal type ?

Apart form "member" what primitive operators would be necessary ?

Mikal