Re: things about grouping

On Thu, Nov 29, 2012 at 8:15 AM, Andrew Welch <andrew.j.welch@xxxxxxxxx> wrote:
>> the comma operator corresponds to union written as | (by definition a
>> set is unordered so the additional ordering constraint imposed by the
>> , operator is meaningless)
>
> The comma is just a way of separating items in sequence, whereas union
> de-dupes and sorts into document order.
>
> select="@foo, @foo, @foo"
>
> vs
>
> select="@foo | @foo | @foo"
>
> the former selects a sequence of 3 items, the latter a sequence of 1.
>

ok but I'm translating , into a set-theoretic construct, in which
domain a,b is indistinct from a|b - correct me if I have got that
wrong.