Compliance with the adversarial principle in arbitral proceedings, within the meaning of artt. 816-bis and 829 co. 1 n. 9 cod. proc. civ., must be assessed in substantive rather than merely formal terms, by ascertaining whether the parties were effectively afforded the opportunity to present their case and to address the issues material to the decision.
The nullity of the arbitral award for breach of the adversarial principle, within the meaning of art. 829 co. 1 n. 9 cod. proc. civ., requires the challenging party to demonstrate the actual prejudice suffered, by identifying the defensive steps that the alleged breach prevented it from taking and their potential bearing on the decision.
The assessment of the evidence and the evidentiary material carried out by the arbitrators is not reviewable in proceedings for the challenge of the arbitral award on the ground of nullity, those proceedings being of limited review and not permitting a re-examination of the merits of the dispute.