Get all possible combinations of the elements in a set

Combinatorics.swift

enum Combinatorics {
    
    
    public static func combinations<T>(of set: Set<T>) -> Set<Set<T>> {
        
        if set.count == 1 {
         
            return Set<Set<T>>([set])
            
        } else {
            
            var allCombinations = Set<Set<T>>()
            
            var diminishedSet = set
            let firstItem = diminishedSet.removeFirst()
           
            for combinationOfDiminishedSet in combinations(of: diminishedSet) {
                
                allCombinations.insert(
                    Set<T>([firstItem])
                )
                allCombinations.insert(
                    combinationOfDiminishedSet.union(Set<T>([firstItem]))
                )
                allCombinations.insert(
                    combinationOfDiminishedSet
                )
            }
            
            return allCombinations
        }
    }
}