A plurality of inventions in the same category may constitute a group of inventions so linked as to form a single general inventive concept. Examples of inventions in the same category are alternative forms of an invention and interrelated inventions.
Alternative forms of an invention may be claimed either in a plurality of independent claims or in a single independent claim (see also F‑IV, 3.7). In the latter case the presence of the two alternatives as independent forms may not be immediately apparent. In either case the same criteria are applied in deciding whether or not there is unity of invention, and lack of unity of invention may therefore also exist within a single claim.
Several independent claims in the same category directed to interrelated subject-matter may meet the requirement of unity even if it appears that the claimed subject-matter is quite different, provided that the special technical features making a contribution over the prior art are the same or corresponding. Examples of such situations include a transmitter and the corresponding receiver, and a plug and the corresponding socket (see also F‑IV, 3.2).
Thus, special technical features relating to the single general inventive concept must be either implicitly or explicitly present in each of the independent claims.