public BankCard CardOn(Timestamp time) => time.CompareTo(this.ValidBefore) >= 0 ? (BankCard) new CardExpired(this.ValidBefore) : this;
public int CompareTo(Timestamp other) => - other.CompareTo(this.Value);
public override Money On(Timestamp time) => time.CompareTo(this.ValidBefore) >= 0 ? Amount.Zero(base.Currency) : this;