Action to set aside an arbitration award. Stabilization of the claim in arbitration. Expansion of the scope of the arbitration after the signing of the terms of reference. Admissibility. Flexibility of the arbitration proceedings. Issues relating to the limits of the arbitration agreement not raised at the party's first opportunity to manifest itself (art. 20 of the Brazilian Arbitration Act). Prohibition of contradictory conduct (venire contra factum proprium). Logical preclusion of the claim to annul the arbitration award: