Presume that a claim defines a composition as comprising substances of Group A in a total amount of 1 - 10%, wherein Group A includes the substances A1, A2 and A3. Limiting claim 1 to the substance A1, i.e. to a composition comprising substance A1 in an amount of 1 - 10% would not exclude the presence of A2 and A3 - even in amounts higher than 10%. A composition with 10% of A1, 10% of A2 and 10% of A3 would be covered by claim 1 as amended but not by claim 1 as granted and therefore contravene Art. 123(3) EPC. According to the technical board of appeal, "This gives rise to a situation in which a way out for the patentee is anything but easy." (Reasons 3.1)
The technical board of appeal proposes the following solution (cited from the headword):
Translated to example mentioned above the claim would read composition comprising substance A1 in an amount of 1 - 10% , wherein the total amount of substances of Group A is 1 - 10%.Where a granted claim directed to a composition defined in an open manner and including the presence of a component belonging to a class or list of compounds in a quantity defined by a range is later amended by limiting the definition of the class or list of compounds, a possible infringement of the requirements of Article 123(3) EPC may be avoided by including in the amended claim a quantitative condition on the limited class or list of compounds and an additional constraint on the total amount of compounds belonging to the broader class or list (point 3.11).