Two-part form unsuitable 

Subject to what is stated in F‑IV, 2.3.2, final sentence, applicants are required to follow the above two-part formulation in their independent claim or claims, where, for example, it is clear that their invention resides in a distinct improvement in an old combination of parts or steps. However, as is indicated by Rule 43, this form need be used only in appropriate cases. The nature of the invention may be such that this form of claim is unsuitable, e.g. because it would give a distorted or misleading picture of the invention or the prior art. Examples of the kind of invention which may require a different presentation are:

the combination of known integers of equal status, the inventive step lying solely in the combination; 
the modification of, as distinct from addition to, a known chemical process e.g. by omitting one substance or substituting one substance for another; and 
a complex system of functionally interrelated parts, the inventive step concerning changes in several of these or in their interrelationships. 

In examples (i) and (ii), the Rule 43 form of claim may be artificial and inappropriate, whilst in example (iii) it might lead to an inordinately lengthy and involved claim. Another example in which the Rule 43 form of claim may be inappropriate is where the invention is a new chemical compound or group of compounds. It is likely also that other cases will arise in which the applicant is able to adduce convincing reasons for formulating the claim in a different form.

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