//
scala> "abcd".toSet.subsets.toSeq
val res1: Seq[Set[Char]] =
List(Set(),
Set(a), Set(b), Set(c), Set(d),
Set(a, b), Set(a, c), Set(a, d), Set(b, c), Set(b, d), Set(c, d),
Set(a, b, c), Set(a, b, d), Set(a, c, d), Set(b, c, d), Set(a, b, c, d))