isSubsetOf package:rio

isSubsetOf :: Ord a => Set a -> Set a -> Bool
rio RIO.Set
O(m*log(n/m + 1)), m <= n. (s1 `isSubsetOf` s2) indicates whether s1 is a subset of s2. 
s1 `isSubsetOf` s2 = all (`member` s2) s1
s1 `isSubsetOf` s2 = null (s1 `difference` s2)
s1 `isSubsetOf` s2 = s1 `union` s2 == s2
s1 `isSubsetOf` s2 = s1 `intersection` s2 == s1