The defence of set-off may be raised as a ground for opposition to enforcement proceedings based on an arbitral award as an enforcement title only where the credit relied upon for set-off arose after the formation of the award, being otherwise precluded by the res judicata arising from the arbitral decision, which prevents the assertion of extinctive or impeaching facts contrary thereto. The failure to raise the defence of set-off in the arbitration proceedings, where the coexistence of the credits occurred in sufficient time to be pleaded pursuant to Article 817 bis of the Code of Civil Procedure, precludes the subsequent opposition by way of set-off in enforcement proceedings, by application of the principle that res judicata covers both that which was pleaded and that which could have been pleaded.