A legal act relating to a sum or value exceeding an amount fixed by decree must be proved in writing under private or notarial signature.
It may only be proved in addition to or against a writing establishing a legal act, even if the sum or value does not exceed that amount, by another writing under private or notarial signature.
A person whose claim exceeds the threshold mentioned in the first paragraph may not be exempted from proof in writing by restricting his claim.
The same applies to a person whose claim, even if less than that amount, relates to the balance or part of a claim exceeding that amount.