Art. 29 O.G.; admissibility of federal appeal in expropriation compensation matters; the Streitwert is determined by the amount actually contested on appeal, and where the opposing party does not challenge the first-instance judgment the threshold cannot be met by reference to the original claim. Compensation for expropriation for local public works, absent a special federal basis, is governed by cantonal public law; it does not arise from a private-law fact pattern and is therefore not subject to the Code of Obligations. The federal Expropriation Act applies only to works undertaken under federal authority or where the Constitution expressly extends it (consid. 2).