Question juridique clé
Whether B.________ had standing to defend as a party to the lease concluded on 10 January 2000 through a simple partnership represented by A.________
Solution extraite
The existing findings did not yet establish B.________'s standing to defend; the case had to be remitted for further factual findings on whether the simple partnership existed already before the lease was concluded.
Motifs extraits
A tacit simple partnership could in principle be inferred from the use of the letterhead, but the evidence was insufficient to show that B.________ was already associated with A.________ on 10 January 2000, which was required for representation under Art. 543(3) CO. Later participation did not make him a party to the lease.