Marc LeBrun <mlb@fxpt.com> wrote:

Am I confused?

No, of course not. I thought x and y could be any integers. From "{x + y SqrtD; integer x, y, D>=0}" I interpreted the ">=0" as applying only to D, not to x and y. Perhaps Z^{+}[\sqrd{D}] would be a better notation for what you have in mind. "*" often denotes something to do with multiplication, usually to just exclude zero. And ( ) usually allows quotients, while [ ] denotes a Z-module. Anyway, my answer applies only if x and y can be any integers, positive, negative, or zero. John Robertson