object Main extends App {
  val xs= 1 to 20 toList
  def drop_odds(list:List[Int])=list.filter(_% 2==0)
  def filter_nth(list:List[Int],n:Int)=list.zipWithIndex.filter { case (_, i) => (i + 1) % n != 0 }.map { _._1}
  def reverse_two_halves(list:List[Int])=list.splitAt(list.length/2) match{case (left:List[Int],right:List[Int])=>right++left}
 
 
  println(drop_odds(xs))
  println(filter_nth(xs,3))  
  println(reverse_two_halves(xs))
 
}
 

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