The distinction between allowable amendments to the content of a European patent application and amendments which are at variance with Art. 123(2) or Art. 76(1) is set forth in H‑IV, 2, and C‑IX, 1.4. These guidelines will be applied mutatis mutandis in the course of opposition proceedings to determine whether the subject-matter of the European patent as granted or as amended during the opposition proceedings extends beyond the content of the application as filed.