Action to annul an arbitral award. Failure to comply with the arbitrator's duty of disclosure (Article 14, §1º, of the Brazilian Arbitration Act). An arbitrator who came to sit on an arbitral tribunal with the lawyer who had appointed her to an arbitration while that arbitration was still ongoing. The duty of disclosure subsists for the duration of the arbitration. Omission of a fact capable of casting doubt on impartiality: