Questão jurídica principal
Whether the tenant validly invoked set-off within the grace period under Art. 257d CO
Decisão extraída
Set-off was timely invoked because the tenant expressly raised it by letter before the expiry of the 30-day grace period.
Fundamentação extraída
Under Art. 124 CO and the case law on Art. 257d CO, the debtor must clearly declare the intention to set off before the deadline; that requirement was met here.