Re: Is {{}} a valid construct?

> > > > 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.

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.

Better yet, how would one create/select {{}} within a relational database or similar? Received on Sat Feb 03 2007 - 02:46:47 CET