It'd be nice to have a method that returns an array, or iterable, of sets that are all the permutations of the elements of the set (a.k.a. the power set)
e.g.
const setA = new AdvancedSet(1, 2, 3)
setA.powerSet() // [AS(), AS(1), AS(2), AS(3), AS(1, 2), AS(1, 3), AS(2, 3), AS(1, 2, 3)]
