Selecting the closest prior art selection in the problem solution approach is not always straight forward. In this appeal decision that starts from a decision of the Examination Division, the Board analyses under what circumstances a closest prior art having a similar purpose may be selected if also another prior art document is available that has the same purpose.
The Board introduced a nice metaphor for the invention of this appeal: Assume the invention is making a salami sandwich. And if there are two relatively close prior arts available, one relating to making a ham sandwich (similar purpose) and the other one making a salami sandwich (same purpose). Then the Board is of the opinion that the prior art relating to making a ham sandwich may be selected if the difference between the selected prior art and the invention is not inventive. Thus, for this metaphor: the difference between the selected prior art with the similar purpose is "introducing salami on the sandwich", and if this difference feature is not inventive, the prior art relating to the ham sandwich may also be selected as the closest prior art. In the metaphor of the ham and salami sandwich, it seems that, according to the board, introducing salami on the sandwich is not really inventive because the skilled person who starts from a ham sandwich and who tries to solve the problem of "making a salami sandwich", would put salami on the sandwich (...unless there are technical difficulties to do that...). The first half of the decision relates to the prior art selection and whether "the salami" is inventive.
After the selection of the closest prior art, four difference features are identified between the closest prior art and the claimed invention. Each feature is discussed separately and each individual features is considered not to be inventive. If you are interested in a discussion of features of a method of manufacturing a semiconductor substrate, one should also read the second half of the decision.