Re: Is {{}} a valid construct?

Neo wrote:
> > > > > Can an empty set contain an empty set?
> >
> > > > If a set contains an element, be it the empty set or not,
> > > > its not the empty set.
> > > > So put your one empty bag of potatoes into your other
> > > > empty bag of potatoes. And wush your second bag is not
> > > > empty anymore. You see, it contains the first empty bag.
> >
> > > Thanks, however I am still confused as Bod Badour in
> > > comp.database.theory has the following reply to your post:
> >
> > The two answers say the same thing.
>
> Do'h! time to untunnel my vision B(
>
> > Why are you confused?
>
> Prior to putting one bag inside the other, there were two empty bags
> meaning two empty sets. How could this be? Set theory says otherwise.

Because a bag is a metaphor, not a set.

> My explanation is that a set is only defined by its elements and does
> not include the container (ie {} or bag). Thus if there aren't any
> elements, there is no set, not even an empty set. Only then can two
> separate empty bags be considered equivalent.

Sets don't have "containers". The empty set is most certainly a set. You can't argue by metaphor.

> Better yet, how would one create/select {{}} within a relational
> database or similar?

What makes you think that a relational database provides a complete model for ZFC?

-- 
David Marcus