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 F-V, 3.2.1 and F-V, 3.2). In the case of a claim defining (chemical or non-chemical) alternatives, i.e. a so-called "Markush grouping", unity of invention is considered to be present if the alternatives are of a similar nature and can fairly be substituted for one another (see F-V, 3.2.5).[Art. 84; Art. 82; ]