1.2 Limits on the obligation to undertake examination 

However, the obligation to undertake such examination must be kept within limits in the interests of procedural expediency. For example, in opposition proceedings, an offer to prove that an alleged public prior use took place will not be taken up if the opponent making such an allegation has ceased to participate in the proceedings and the necessary evidence cannot be easily obtained at a reasonable cost.

The unity of the subject-matter of the European patent is not to be examined in opposition proceedings (G 1/91, see D‑V, 2.2).