In T 647/97 the board stated that the invention or subject-matter of a previous application was to be considered the same as that of a subsequent application if the disclosure of both applications was the same. This 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.
For a further example, see T 782/07.