Problem with Coursera Scala video 3.1 code

gistfile1.txt

package objsets

abstract class IntSet {
  def incl(x:Int): IntSet
	def contains(x:Int): Boolean
}


class Empty extends IntSet {
	def contains(x: Int): Boolean = false
	def incl(x: Int): IntSet = new NonEmpty(x, new Empty, new Empty)
}

class NonEmpty (elem: Int, left: IntSet, right: IntSet) extends IntSet {
	def contains(x: Int):Boolean =
		if (x < elem) left contains x
		else if (x > elem) right contains x
		else true
		
	def incl(x:Int):IntSet =
		if (x < elem) new NonEmpty(elem, left incl x,right)
		else if (x > elem) new NonEmpty(elem, left, right incl x)
		else this
		
	//override def toString = "{" + left + elem + right + "}"
}

object Video1 {
	val empty = new Empty
	empty.contains(2)
}