abstract class IntTree 

case object EmptyTree extends IntTree 

case class Node(elem: Int, left: IntTree, right: IntTree) extends IntTree 

def contains(t: IntTree, v: Int): Boolean = t match {
  case EmptyTree => false
  case Node(x,l,r) => if (x == v) true 
		      else if (v < x) contains(l,v) 
		      else contains(r,v)
}