# Universal set question

1. Sep 13, 2005

### Kamataat

Let's say I have to prove something about two sets and I want to make use of the notion of the universal set. Is it OK then to define the universal set as the union of these two sets?

- Kamataat

2. Sep 13, 2005

### EnumaElish

Last edited: Sep 14, 2005
3. Sep 13, 2005

### phoenixthoth

4. Sep 14, 2005

### philosophking

Wouldn't you also have to union (in addition to the two sets) the intersection of the complements of the two sets?