Power Set

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The elements of a power set are themselves sets.
The power set of a set is the set of all the subsets of that set.

Example
The set {a, b} has 2 members: a and b.
{a, b} has two obvious subsets: {a} and {b}.
But the empty set and {a, b} itself are also subsets.
So the power set is a set with 4 members:
    { {}, {a} , {b} , {a, b} }
As usual, the order is not important
but it is easiest to list the members by imposing an order.