The judgment by which the ordinary court, upholding the defence of arbitration agreement, declines its own jurisdiction in favour of the arbitrators is challengeable exclusively by means of the compulsory reference on jurisdiction pursuant to Articles 819-ter, paragraph 1, and 42 of the Code of Civil Procedure, irrespective of the formal qualification attributed by the court to its own ruling, with the consequence that the appeal brought against such decision must be declared inadmissible.