While an independent claim is always part of the common matter among its dependent claims, the opposite is not true: a claim dependent on several independent claims is never part of the common matter between these independent claims.
For example, an application contains three independent claims, A, B and C, and several claims combining the content of the independent claims, i.e. claims A+B, A+C, B+C and A+B+C.
Independently of the order and the manner in which the claims are presented, the application in question contains three sets of claims:
Unity or lack of unity is assessed firstly between the independent claims A, B and C: if these claims are not linked by a single general inventive concept and they do not contain any same or corresponding special technical features, a lack of unity is present. The content of any of the dependent claims, e.g. of claim A+B+C, has no bearing on this analysis. Dependent claims comprising features of two or more groups of inventions, i.e. dependent claim A+B+C in the above examples, belong to all of the two or more groups of inventions.
Source: http://www.epo.org/law-practice/legal-texts/html/guidelines/e/f_v_3_2_4.htm
Date retrieved: 17 May 2021