1. Beginning of the examination of the opposition

2. Extent of the examination

3. Non‑patentability pursuant to Art. 52 to 57

4. Insufficient disclosure of the invention

5. Clarity of claims

If the patent proprietor, when replying to the notice of opposition, contends that the opposition is inadmissible pursuant to Rule 77(1) and Rule 77(2) because of deficiencies specified by the patent proprietor himself, the opponent concerned must be given the opportunity to submit comments within a period fixed by the formalities officer (normally two months).

If the opposition division concludes that the opposition is inadmissible, it must as a

Amended documents must, provided that it is not irrelevant at the stage reached in the procedure, be as complete as possible and drawn up in such a way as to allow the European patent, where appropriate, to be maintained without further delay in the amended version.

These considerations apply also to auxiliary requests in which the patent proprietor proposes amendments for consideration by the opposition division only if the division is unable to grant the main request, for example that the opposition is to be rejected.

Since the admissibility of an opposition is always open to question by the patent proprietor, no separate communication that the opposition is admissible will be sent to the opponent or the patent proprietor.

Under Art. 101(1) and Rule 79(1), the examination as to whether the European patent can be maintained can only be performed if at least one admissible opposition has been filed. This means that the opposition division has to refrain from commenting on the substantive merits of the opposition when expressing an opinion on its inadmissibility if there is no further admissible opposition (see T 925/91).