paragraph 323 in volume 3, chapter 21, The Oral Proceedings
Only after the written proceedings are completed are the parties in a position to determine whether they require calling witnesses and experts as part of their oral presentations. By Article 57 of the Rules:
Without prejudice to the provisions of the Rules concerning the production of documents, each party shall communicate to the Registrar, in sufficient time before the opening of the oral proceedings, information regarding any evidence which it intends to produce or which it intends to request the Court to …