I am studying what sets are ...

And what I have learned is that we have "sets" and in those sets there are "elements"

So a set can be defined with {}

And if a set has no elements this is an emty set = ∅

So a set can be defined with elements 1, 3, 6 = {1, 3, 6}

But if we have the following set:

{{1,2,{3},{4,5},6,{{7},8}},9}

How do we determine how many elements there are in this set?

I would say 9 ... (1, 2, 3, 4, 5, 6, 7, 8, 9)

Or is it 2? (6, 9)

Or is this 7? (5 sets that can be seen as elements and 2 numbers)

Thanks in advance ...