Paragraph 17

issue is joined on a notice of opposition to the grant of a patent under section 14 of the 1949 Act when the applicant for the patent files a counter-statement fully setting out the grounds on which the opposition is contested;

issue is joined on an application for the revocation of a patent under section 33 of that Act when the patentee files a counter-statement fully setting out the grounds on which the application is contested.