Art. 30 OG; timeliness of appeal to the Federal Court. The statutory twenty-day period is peremptory and must be examined ex officio. The appeal is only timely if the declaration is lodged with the competent cantonal court within the deadline; neither signature nor dispatch by post suffices. Proof of service by official certificate prevails over a contrary assertion by the appellant. An appeal filed on the 21st day after notification is inadmissible and is not examined on the merits (consid. 1-2).