op(x: MyType, y: MyType): Option[List[MyType]] {
  if(x > y) Some(List(x, y))
  else if(x == y) Some(List(x))
  else None
}

for (a <- z) {
  l.map {
    e => op(e, a) match {
      case Some(head :: Nil) => head
      case Some(head :: tail :: Nil) => //TODO want this to be part of List[MyType]
      case None => // TODO -- ignore ? switch to flatMap
    }
  }
}