The boards of appeal use the problem and solution approach to determine whether an inventive step is involved. This requires analysis of the invention in terms of a technical solution to a technical problem. Since both the solution and the problem solved by an invention have to be of a technical nature, the problem and solution approach might raise questions when the invention comprises non-technical aspects or elements. Such difficulties are to be resolved by taking due care to define the technical field to which the invention belongs, the scope of technical expertise and skills expected to be applied by the technical person in that particular technical field, and the correct formulation of the technical problem actually solved (T 1177/97). Such an approach must necessarily differentiate between technical and non-technical features when applied to "mixed" or hybrid inventions (T 1543/06).