To avoid ambiguity, particular care should be is exercised when assessing claims which employ the word "in" to define a relationship between different physical entities (product, apparatus), or between entities and activities (process, use), or between different activities. Examples of claims worded in this way include the following:
In examples (i) to (iii) the emphasis is on the fully functioning sub-units (cylinder head, dial tone detector, method for controlling the arc welding current and voltage) rather than the complete unit within which the sub-unit is contained (four-stroke engine, telephone, process). This can make it unclear whether the protection sought is limited to the sub-unit per se, or whether the unit as a whole is to be protected. For the sake of clarity, claims of this kind must should be directed either to "a unit with (or comprising) a sub-unit" (e.g. "four-stroke engine with a cylinder head"), or to the sub-unit per se, specifying its purpose (for example, "cylinder head for a four-stroke engine"). The latter course may be followed only at the applicant's express wish and only if there is a basis for it in the application as filed, in accordance with Art. 123(2).
With claims of the type indicated by example (iv), the use of the word "in" sometimes makes it unclear whether protection is sought for the improvement only or for all the features defined in the claim. Here, too, it is essential to ensure that the wording is clear.
However, claims such as "use of a substance ... as an anticorrosive ingredient in a paint or lacquer composition" are acceptable on the basis of second non-medical use (see G‑VI, 7.2, second paragraph).