When the parties confer the power of appointment of arbitrators upon the Judicial Authority through contractual clause, the latter is invested with such power not directly by law but by the free and lawful will of the parties. In presence of a clause which attributes the power of appointment to a specific Judicial Authority, it is not necessary to resort to the legal criteria for determination of jurisdiction by subject matter, which would intervene instead only in absence of the arbitration clause and of the relative contractual provision.