Rule 117

Where the European Patent Office considers it necessary to hear a party, witness or expert, or to carry out an inspection, it shall take a decision to this end, setting out the investigation which it intends to carry out, relevant facts to be proved and the date, time and place of the investigation. If the hearing of a witness or expert is requested by a party, the decision shall specify the period within which the requester must make known the name and address of any witness or expert concerned.