unionWith package:non-empty

unionWith :: Ord k => (a -> a -> a) -> T k a -> T k a -> T k a
non-empty Data.NonEmpty.Map
forAllNonEmptyMap $ \xs -> forAllNonEmptyMap $ \ys -> Map.unionWith (++) (NonEmptyMap.flatten xs) (NonEmptyMap.flatten ys) == NonEmptyMap.flatten (NonEmptyMap.unionWith (++) xs ys)