Action to annul an arbitration award. Allegation of violation of the adversarial principle and the right to a full defense in the arbitration proceedings. Absence of proof. Dispensability of closing arguments and accounting expert evidence in light of the evidence already produced in the arbitration proceedings. Prevalence of the presumption of validity of the arbitration award. Assessment of evidence as an activity exclusively within the arbitrator's purview. Impossibility of review by the judiciary: