Article 54 of Code of Civil Procedure

The litigants shall appear in person on the day designated for hearing the action, or lawyers whom they appoint shall appear on their behalf. The court may accept as their representative a person whom they choose who is related to them by marriage, kinship or affinity up to the fourth degree. The representative must establish his authority to represent his principal. Submission of a document to that effect shall suffice to establish the authorization; if it is not an official document, the principal's signature must be authenticated. Authorization may be given at the hearing by a declaration recorded in its minutes, in which case the declaration shall take the place of authentication of the signature. Where there are several representatives, any one of them may act alone in the case unless prohibited from doing so by the terms of the authorization. Article 55 (2) As soon as authorization is issued by a litigant, his representative's domicile shall be recognized for service of the papers necessary for conducting the action at all levels of litigation at which it is heard, unless the authorization is restricted to a particular level. The representative's withdrawal or dismissal shall not prevent proceedings from continuing against him unless the said litigant serves notice on the other litigant of the appointment of a replacement or of his intention to conduct the action himself. The representative may not withdraw from the representation at an inappropriate time.