Facts
The brothers [C.] (deceased) and [A.] (the appellant) were shareholders of the now bankrupt [D. GmbH]. The [B. AG] (the plaintiff, the respondent) had business relations with [D. GmbH] and [C.].
On December 16, 2002, the parties concluded a "Credit Agreement with Assumption of Debt". Therein, the [B. AG] granted a current account credit to [D. GmbH], and [D. GmbH] assumed a loan debt of [C.] in the amount of CHF 230,000.--. The appellant and [C.] were jointly and severally liable for this.
After the bankruptcy of [D. GmbH], the [B. AG] pursued the appellant based on the credit agreement for the realization of the mortgage. The appellant disputed having signed the credit agreement in the present version.
Considerations
The lower court considered that according to Art. 178 CPC, the party relying on a document must prove its authenticity if its authenticity is disputed by the other party. However, the dispute must be sufficiently substantiated by presenting specific circumstances that raise serious doubts about the authenticity of the document's content or signature.
The lower court concluded that…