Amend patent claim in opposition due to lack of clarity

Question

I'm doing some exercises from the EPO and struggle at this one:

In opposition proceedings a patent proprietor has proposed amendments to claims 1, 3 and 4 of its patent to overcome issues of novelty and inventive step. The proprietor has also noted a problem with the clarity of claim 2 and has additionally proposed an amendment to this claim. Is the amendment of claim 2 permitted?

1. Yes
2. No

The answer is:

The correct answer is 2. Amendment of claim 2 is not permitted because the amendment is not occasioned by a ground for opposition (since clarity is not a ground for opposition as specified by Article 100 EPC) (Rule 80 EPC, implementing Article 101(1) EPC).

I don't get this. When I look at Article 100:

(b) the European patent does not disclose the invention in a manner sufficiently clear and complete for it to be carried out by a person skilled in the art;

it should be amendable. Going further to Rule 80:

Without prejudice to Rule 138, the description, claims and drawings may be amended, provided that the amendments are occasioned by a ground for opposition under Article 100, even if that ground has not been invoked by the opponent.

for me it reads like 100 b) is a reason to amend claim 2 due to Rule 80? Having a look at Article 101 (1):

If the opposition is admissible, the Opposition Division shall examine, in accordance with the Implementing Regulations, whether at least one ground for opposition under Article 100 prejudices the maintenance of the European patent. During this examination, the Opposition Division shall invite the parties, as often as necessary, to file observations on communications from another party or issued by itself.

does not bring up any reason against it, at least not from my understanding. Though I don't understand the sense of Article 101 (1) in this context, here.

Answer 1

Looks like you got confused because you read the word 'clear' in Art. 100(b) EPC. The Article refers to the claims being enabled, the description must be an enabling disclosure. The ground of Art. 100(b) EPC relates to the patentability requirement of Art. 83 EPC: 'The European patent application shall disclose the invention in a manner sufficiently clear and complete for it to be carried out by a person skilled in the art. '

The clarity requirement that claims must comply with is laid down in Art. 84 EPC: 'The claims shall define the matter for which protection is sought. They shall be clear and concise and be supported by the description.'

Among the grounds for opposition laid down in Art. 100 EPC you will not find a ground to the requirements of Art. 84 EPC because there is none. And without said ground, you are forbidden from making the amendment you want to make due to Rule 80 EPC.

What Art. 101(1) EPC specifies is that any opposition must be examined to find out if the European Patent has been correctly granted in view of the grounds put forward by the opponent. In a nutshell, that is an opposition. The second pat of Art. 101(1) EPC is the legal basis for the opponent, the proprietor and the EPO typically to provide their view, during the opposition proceedings, on whether the European Patent can be maintained as is or in amended form. I am unable to see the link between the question about amendments you have and Art. 101(1) EPC though.