Concerning the requirement of the same invention or subject-matter (cf. Art. 87(1) and (4) EPC), according to T 647/97 it was not only required that the solution to a given problem (i.e. the features of the main claim) was the same, but also that the problem itself was the same in both applications. The proper definition of the problem to be solved in the priority document as understood by the skilled person reading the document with his common general knowledge in the art at its filing date was decisive to that end. The board noted that the priority document only mentioned solid and gel copolymer compositions for providing a sustained-release composition for treating periodontal disease (first problem), but was silent about any fluid or liquid compositions. The skilled person would moreover not consider fluid and liquid compositions as a suitable solution for the problem addressed in the priority document. It was only disclosed in the contested patent that the fluid and liquid compositions surprisingly transformed into a near solid phase and would therefore be suitable for treating difficult to reach areas of periodontal cavities (second problem). It therefore constituted a second invention involving a different problem and a different solution.
In T 837/13 the patent and the priority document aimed at solving technical problems of the Palmaz-Schatz stent (low stent-to-vessel ratio uniformity, comparative rigidity, limited flexibility), the problem posed in the patent being identical to one posed in the priority document. The appellant objected that the priority document solved a second problem not even addressed in the patent (provision of a wide range of design options). The board stated that there was no reason why the priority-claiming application would need to solve all problems raised in the priority document. It could well relate to only one aspect of the disclosure in the priority document. What could be objected to - see T 647/97 - was a situation where the priority-claiming application solved a new problem different and not derivable from that posed in the priority document. This did not apply here.
For a further example, see T 782/07.