type InitialTimestamp extends Number {
validate() { initial(this, now) }
}
// Returns true if the value is intialized to init, or retains it's prior
// value, otherwise.
initial(value, init) { value == (prior(value) == null ? init : prior(value)) }
can be
type InitialTimestamp extends Number {
validate() { prior(value) == null ? this == now : this == prior(this) }
}
can be