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I implemented the powerset function:
powerset({abc}) = { {}, {a}, {b}, {c}, {a, b}, {a, c}, {b, c}, {a, b, c} }
import Data.Set (fromList, toList)
import Data.List (sort)
powerset :: (Ord a, Eq a) => [a] -> [[a]]
powerset xs = toList . fromList . (map sort) $ xs : [] : f xs ++ map return x...