Question juridique clé
Whether the tenant's teaching activity in the apartment violated the lease and justified extraordinary termination under Art. 257f CO.
Solution extraite
The teaching activity was tacitly accepted for years and was not shown to have become incompatible with the lease; extraordinary termination was not justified on this ground.
Motifs extraits
The general conditions prohibited professional activity unless otherwise agreed. The long-standing, known use since 1986 allowed the tenant to rely in good faith on tacit permission. The record did not prove that the activity later intensified beyond that tacit agreement to a degree requiring cessation.