Originally Posted by

**taypez** The problem is:

Let U={a,b,c}.

Write the power set and an explicitly list of all sigma algebras of subsets of U.

I got the power set to be {{empty set},{a},{b},{c},{a,b},{ac},{abc}}

I know the power set is a sigma algebra. I'm not sure what others are sigma algebras.

Could another one be {{a},{b},{c}}?

Also, if you have a collection of all open intervals on the real line together with all their complememts, would this be a sigma algebra?

Any help on this would be appreciated. Thanks