1. Define the custom property delegate called ObservableVetoableDelegate as a subclass of the ObservableProperty class:

class ObservableVetoable<T>(initialValue: T,
                          val updatePrecondition: (old: T, new: T)
                           -> Boolean,
                          val updateListener: (old: T, new: T)
                           -> Unit) :
        ObservableProperty<T>(initialValue = initialValue) {

    override fun beforeChange(property: KProperty<*>,
                              oldValue: T,
                              newValue: T): Boolean =
            updatePrecondition(oldValue, newValue)

    override fun afterChange(property: KProperty<*>,
                             oldValue: T,
                             newValue: T) = 
            updateListener(oldValue, newValue)
}

2. Define the initialTemperature, updatePrecondition, and updateListener arguments required by the ObservableVetoable class:

val initialTemperature = 1
val updatePrecondition: (Int, Int) -> Boolean =
        { oldValue, newValue -> Math.abs(oldValue - newValue) >= 10 }

val updateListener: (Int, Int) -> Unit = { _, newValue -> println(newValue) }

3. Declare the temperature: Int variable by delegating it to the ObservableVetoable class instance:

var temperature: Int by ObservableVetoable(initialTemperature, 
                                           updatePrecondition, 
                                           updateListener)