class Time2(private[this] var h:Int, private[this] var m:Int){
  require(h > 0 && h < 24 && m > 0 && m < 59)

  def hour:Int = h
  def hour_=(h:Int) {
    require(h > 0 && h < 24)
    this.h = h
  }

  def minute:Int = m
  def minute_=(m:Int) {
    require(m > 0 && m < 59)
    this.m = m
  }

  def before(other:Time2):Boolean =
    other.hour > h || other.hour == h && other.minute > m
}