c) Assessment of inventive step without assessing the prior art 

In T 87/08 the board pointed out that Art. 56 EPC required that the assessment of inventive step be made "having regard to the state of the art". Accordingly, a decision was not sufficiently reasoned if the chain of reasoning to justify the finding of lack of inventive step merely stated that a purported effect had not been achieved, i.e. this technical problem had not been solved, without reformulating the problem in a less ambitious way and without assessing the obviousness of the claimed solution to that reformulated problem in the light of the cited prior art.

In T 2375/10 the board found that since the requirement of inventive step under Art. 56 EPC had to be assessed in the light of the prior art, the decision of the examining division to conclude that there was a lack of inventive step without referring to the prior art was insufficiently reasoned within the meaning of R. 111(2) EPC. See also T 306/09.