According to the established case law of the boards of appeal (see T 654/92, T 691/94, T 87/01, T 730/05, T 1449/05, T 211/06), the prior art cited and acknowledged in a patent application for the purpose of formulating the technical problem may be used as the starting point for assessing novelty and inventive step (T 628/07).
In T 654/92 the board stated that the expression "background art" in the English version of R. 27(1)(b) EPC 1973 was to be interpreted as referring to prior art within the meaning of Art. 54(2) EPC 1973. The practice of starting out from art known to the applicant but not public at the claimed priority date was inconsistent with the requirements of the EPC. Any such art had to be ignored in an assessment of inventive step.
On the question whether an applicant may resile from its indication of background art, either implicitly or explicitly, some boards have taken the view that, unless resiled from or clearly not prior art for other reasons, it may be relied upon as prior art (see T 654/92, T 691/94, T 730/05, T 1449/05, T 1554/05, T 211/06 and T 413/08).
In T 413/08 the board stated in the absence of any indication to the contrary, an acknowledgment of prior art by a patent proprietor might be accepted at face value. If a patent proprietor resiled from an acknowledgment of prior art at a point in time which did not give rise to any procedural problems, the acknowledgement could no longer be relied upon.