Rule 119
Examination of evidence before the European Patent Office

(1) The Examining Division, Opposition Division or Board of Appeal may commission one of its members to examine the evidence adduced. 

(2) Before a party, witness or expert may be heard, he shall be informed that the European Patent Office may request the competent court in the country of residence of the person concerned to re-examine his testimony under oath or in an equally binding form. 

(3) The parties may attend an investigation and may put relevant questions to the testifying party, witness or expert.