static public IEnumerable<Set<T>> SubsetsUnions<T>(this Set<Set<T>> sigmaAlgebra)
{
Set<T> c=new Set<T>();
foreach(bool[] combi in Combination.Combinations(sigmaAlgebra.Count)){
for(int i=0;i<combi.Length;i++){
if(combi[i]){
c.UnionWith(sigmaAlgebra.ElementAt(i));
}
}
yield return c;
}
}