Error:(4, 52) value amt is not a member of Bill
   def compare(that: Bill): Int = (this.amt - that.amt)

import scala.math.Ordered

class Bill(amt : Int) extends Ordered[Bill] {
   def compare(that: Bill): Int = (this.amt - that.amt)
}

object Test extends App {
 val one = new Bill(10)
 val two = new Bill(20)
 println(one < two)

}