Questione giuridica chiave
Whether the buyers' undertaking was a suretyship requiring public deed or a guarantee under Art. 111 CO
Decisione estratta
The undertaking was a guarantee under Art. 111 CO because it was independent of the principal debtor's duty and focused on the creditor's expected benefit.
Motivazione estratta
The decisive criterion is accessoriness. The buyers promised supplementary contributions if the pension target was not reached, regardless of the employer's underlying obligation; the promise was creditor-oriented and independent, so it was not a suretyship.