(11)In the case of mixed contracts, the applicable rules should be determined with respect to the main subject of the contract where the different parts which constitute the contract are objectively not separable. It should therefore be clarified how contracting authorities should determine whether the different parts are separable or not. Such clarification should be based on the relevant case-law of the Court of Justice of the European Union. The determination should be carried out on a case-by-case basis, in which the expressed or presumed intentions of the contracting authority to regard the various aspects making up a mixed contract as indivisible should not be sufficient, but should be supported by objective evidence capable of justifying them and of establishing the need to conclude a single contract. Such a justified need to conclude a single contract could for instance be present in the case of the construction of one single building, a part of which is to be used directly by the contracting authority concerned and another part to be operated on a concessions basis, for instance to provide parking facilities to the public. It should be clarified that the need to conclude a single contract may be due to reasons both of a technical nature and of an economic nature.