Where a purchaser concludes a contract intended to satisfy objectively separable needs which are subject, on the one hand, to the ordinary law on contracts set out in Book I of this Part and its Book II relating to partnership contracts and, on the other hand, to the special legal regime applicable to other public contracts set out in Book V or to other concession contracts set out in Book II of Part Three, this contract is subject to the ordinary law on contracts set out in Book I and Book II relating to partnership contracts of this Part.