    def plus(x: Quantity, y: Quantity): Quantity = Quantity(x.value + y.value)     def minus(x: Quantity, y: Quantity): Quantity = Quantity(x.value - y.value)     def times(x: Quantity, y: Quantity): Quantity = Quantity(x.value * y.value)     def negate(x: Quantity): Quantity = Quantity(-x.value)     def fromInt(x: Int): Quantity = Quantity(x.toDouble)     def toInt(x: Quantity): Int = x.value.toInt     def toLong(x: Quantity): Long = x.value.toLong     def toFloat(x: Quantity): Float = x.value.toFloat     def toDouble(x: Quantity): Double = x.value     def compare(x: Quantity, y: Quantity): Int = x.value compare y.value 