In W 6/97 it was held that the determination of unity of invention must be made on the basis of the contents of the claims as interpreted in the light of the description and of the drawings, if applicable (with reference to Annex B, Part 1(b) PCT Administrative Instructions; cf. now Annex B, para. (b) PCT Administrative Instructions, as in force from 1.1.2022).
In W 39/90 the board observed that it was not the formal choice of words or form of reference, but the actual content of the claims which established technical relationships between the subject-matter of different claims, and which was thus decisive for the question of unity. In W 33/92 the board emphasised that R. 13.1 PCT did not require the link between the subject-matter of the two independent claims to be expressly stated in their wording. All that was required was that there be a single inventive concept.