(1) Within nine months after publication of the grant of a patent any person may give notice of opposition to the patent, in the case of usurpation only the aggrieved party. Notice of opposition is to be given in a written reasoned statement. It may only be based on the claim that one of the grounds for revocation set out in section 21 exists. The facts justifying the opposition must be detailed. The particulars, insofar as they have not already been included in the notice of opposition, are to be submitted in writing within the opposition period.
(2) Where a notice of opposition to a patent has been given, any third party who can prove that an action has been brought against them on account of an infringement of the patent may intervene in the opposition proceedings as an opponent after the expiry of the opposition period if they give notice of intervention within three months after the date on which the action claiming the infringement was filed. The same applies to any third party who can prove that, following a demand by the proprietor of the patent that the third party refrain from the alleged infringement of the patent, they instituted proceedings for a ruling that they are not infringing the patent. The notice of intervention is to be declared in writing and reasoned within the time limit referred to in sentence 1. Subsection (1) sentences 3 to 5 applies accordingly.
(3) A hearing is held in the opposition proceedings upon the request of a party or if the Patent Division deems this to be expedient. When issuing the summons, the Patent Division is, as a rule, to draw attention to the points which in its opinion need to be discussed for the purposes of the decision to be taken. The hearing, including delivery of the decision, is public. Section 169 (1) sentence 2 and sections 171b to 175 of the Courts Constitution Act (Gerichtsverfassungsgesetz) apply accordingly, with the proviso that the public may also be excluded from the hearing at the request of one of the parties if there is concern that the interests of the applicant meriting protection are at risk.
(4) The chair of the Patent Division ensures that order is maintained during the hearing and thus exercises domestic authority.
(5) In all other cases, section 43 (3) sentence 2 and sections 46 and 47 apply accordingly in the opposition proceedings.