object Test{ def main(args : Array[String]): Unit = { import scala.collection.immutable.TreeSet; val mainSet = TreeSet(1 to 5 :_*) var compareCalled = false; val smallerSet = TreeSet(2 to 4 :_*)(Ordering[Int].reverse) println(mainSet.mkString(",")) println(smallerSet.mkString(",")) println(smallerSet.subsetOf(mainSet)); } }