How do you calculate the power set of a set of sets?

[cilla]

How are you supposed to go about putting together the power set of a set of sets such as
X = {{1},{1,2}}

What is the power set of X then? And what's the rule for calculating cardinality for the power set of a set that consists of elements which are sets such as the above? Because the set X to my understanding has 2 elements, both of which are sets... so the power set of X doesn't consist of only 4 elements, does it?

There are:
{}, {1}, {1,2}, {{1},{1,2}}

Or is that really all?

Please help clarify this to me, thanks so much.

 

[da_nang]

Yep, that's about it. You only care about finding the subsets of X so the element a_i \in X can be whatever.

 

[gopher_p]

Actually, the singletons of X here are {{1}} and {{1,2}}. It's a subtle but important distinction.

 

[cilla]

Oh yes, thank you gopher_p (and da_nang). I'm just glad it's not some crazy mix of inner and outer elements.

 

[caveman1917]

If the iterated set notation confuses you, just do something like $a = \{1\}, b = \{1, 2\}, X = \{a,b\}$ and then at the end substitute back.