In the absence of the express written stipulation required by art. 808 ter cod. proc. civ., whereby the parties provide that the dispute is to be determined by the arbitrators by way of contractual determination, the arbitration must be regarded as arbitration proper and the provisions on arbitration proper apply. A provision that the sole arbitrator is to decide ex aequo et bono is not in itself an indicator that the arbitration is contractual arbitration. A reference in the arbitration clause to the rules of an arbitral chamber which provide for the resolution of disputes by arbitration proper unless the parties expressly agree otherwise constitutes a clear expression of the intention to have recourse to arbitration proper, with the consequent lawfulness of the decree declaring the award enforceable.