Art. 56 OG; Art. 231 OR; jurisdiction over damages claims from non-performance of a real-estate sale. Where the claim for compensation is based on the alleged non-performance of a contract for the sale of immovable property, cantonal law governs both the existence and extent of any damages claim under Art. 231(1) OR. Such a dispute concerns exclusively cantonal private law and is therefore not cognizable by the Federal Court on appeal under Art. 56 OG (consid. 1).