A claim, whether independent or dependent, may refer to alternatives, provided that the number and presentation of alternatives in a single claim does not make the claim obscure or difficult to construe and provided that the claim meets the requirements of unity (see also III, 7.4 and III, 7.8). In case of a claim defining (chemical or non-chemical) alternatives, i.e. a so-called "Markush-grouping", unity of invention should be considered to be present if the alternatives are of a similar nature and can fairly be substituted for one another (see III, 7.4a).