Key legal question
Whether Art. 423(1) CO applies to undisclosed, unauthorized subletting during the lease term.
Extracted holding
Yes. A tenant who sublets without authorization and in bad faith manages the landlord's affairs imperfectly and must surrender the profits.
Extracted reasoning
The tenant knowingly concealed the true sublease terms by sending a false contract; this showed awareness that he lacked authorization and was profiting unlawfully from the landlord's property.