A claim may also contain a reference to another claim even if it is not a dependent claim as defined in Rule 43(4). One example of this is a claim referring to a claim of a different category (e.g. "Apparatus for carrying out the process of claim 1 ...", or "Process for the manufacture of the product of claim 1 ..."). Similarly, in a situation like the plug and socket example of F‑IV, 3.2(i), a claim to the one part referring to the other co-operating part (e.g. "plug for co-operation with the socket of claim 1 ...") is not a dependent claim. In all these examples, the examiner should carefully consider the extent to which the claim containing the reference necessarily involves the features of the claim referred to and the extent to which it does not. Indeed, objections on the grounds of lack of clarity and failure to state the technical features (Rule 43(1)) apply to a claim which simply says "Apparatus for carrying out the process of Claim 1". Since the change of category already makes the claim independent, the applicant should be required to set out clearly in the claim the essential features of the apparatus.
For claims directed to computer-implemented inventions, in which independent claims often comprise references to other independent claims, see F‑IV, 3.9.
The subject-matter of a claim in one category may also to some extent be defined in terms of features from another category; therefore an apparatus may be defined in terms of functions it is able to perform, provided the structure is made sufficiently clear; or a process may be defined in terms of essential structural features of the apparatus for carrying it out; or an element of an apparatus may be defined in terms of how it is made. However, in the wording of these claims and in the assessment of the claimed subject-matter, a clear distinction must be maintained between product claims (for a device, apparatus or system) and process claims (for a process, activity or use). For example, a claim for an apparatus cannot normally be limited only by the manner in which the apparatus is used; for this reason, a claim which simply reads "Apparatus Z, when used for carrying out process Y" should also be objected to on the grounds of lack of clarity and failure to state the technical features (Rule 43(1)).
In the case of a claim for a process which results in the product of a product claim, if the product claim is patentable then no separate examination for the novelty and non-obviousness of the process claim is necessary, provided that all features of the product as defined in the product claim inevitably (see also G‑VII, 13) result from the claimed process (see F‑IV, 4.5, and T 169/88). This also applies in the case of a claim for the use of a product, when the product is patentable and is used with its features as claimed (see T 642/94). In all other instances, the patentability of the claim referred to does not necessarily imply the patentability of the independent claim containing the reference. It should also be noted that if the process, product and/or use claims have different effective dates (see F‑VI, 1 and F-VI, 2), a separate examination may still be necessary in view of intermediate documents (see also G‑VII, 13).