Question: all possible sigma algebra in finite set

Dear all 
I have a finite set, I would like to compute all possible sigma algebra

Using the following code ( thanks to vv), for helping me to use this code:

sigma_algebra_all.mw 

 

This code give me the sigma algebra if I fix the generator of the sigma algebra, How can I find all possible sigma algebra in the global set {1,2,3}

 

Thank you

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