BitSet: List(invariant, invariant, invariant, invariant)
HashSet: List(covariant (true), covariant (true), covariant (true), covariant (true))
ListSet: List(covariant (true), covariant (true), covariant (true), covariant (true))
SortedSet: List(invariant, invariant, invariant, invariant)
TreeSet: List(invariant, invariant, invariant, invariant)
ValueSet: invariant