In the context of the problem-solution approach, it is permissible to combine the disclosure of one or more documents, parts of documents or other pieces of prior art (e.g. a public prior use or unwritten general technical knowledge) with the closest prior art.

Section GL/EPO G‑VII, 5.4.1, in the Guidelines for Examination in the EPO applies mutatis mutandis.

In the third stage the question to be answered is whether there is any teaching in the prior art as a whole that would (not simply could, but would) have prompted the skilled person, faced with the objective technical problem, to modify or adapt the closest prior art while taking account of that teaching, thereby arriving at something falling within the terms of the claims, and thus achieving what the invention achieves.[GL/ISPE A13.08.8;

Generally, the principles laid down in section GL/EPO G‑VII, 5.1, in the Guidelines for Examination in the EPO apply mutatis mutandis. The closest prior art is that which in one single reference discloses the combination of features which constitutes the most promising starting point for a development leading to the invention.

Thus the question to consider, in relation to any claim defining the invention, is whether before the filing or priority date valid for that claim, having regard to the art known at the time, it would have been obvious to the person skilled in the art to arrive at something falling within the terms of the claim. If so, the claim is not allowable for lack of inventive step.