Rule 118
Summons to give evidence before the European Patent Office

(1) A summons to give evidence before the European Patent Office shall be issued to the parties, witnesses or experts concerned. 

(2) At least two months' notice of a summons issued to a party, witness or expert to testify shall be given, unless they agree to a shorter period. The summons shall contain: 

(a) an extract from the decision under Rule 117, indicating the date, time and place of the investigation ordered and stating the facts in respect of which parties, witnesses or experts are to be heard;

(b) the names of the parties and particulars of the rights which the witnesses or experts may invoke under Rule 122, paragraphs 2 to Rule 122, paragraphs 4;

(c) an indication that the party, witness or expert may request to be heard by a competent court of his country of residence under Rule 120, and an invitation to inform the European Patent Office, within a period to be specified, whether he is prepared to appear before it.