Article 9
(1) The parties are bound by any usage to which they have agreed and by any practices which they have established between thæuselves.
(2) The parties are considered, unless otherwise agreed, to have impliedly made applicable to their contract or its formation a usage of which the parties knew or ought to have known and which in international trade is widely known to, and regularly observed by, parties to contracts of the type involved in the particular trade concerned.
Article 10
For the purposes of this Convention:
(a) if a party has more than one place of business, the place of business is that which
has the closest relationship to the contract and its performance, having regard to the circumstances known to or contemplated by the parties at any time before or at the conclusion of the contract;
(b)
if a party does not have a place of business, reference is to be made to his habitual residence.
Article 11
A contract of sale need not be concluded in or evidenced by writing and is not subject to any other requirement as to form. It may be proved by any means, including witnesses.
Article 12
Any provision of article 11, article 29 or Part II of this Convention that allows a contract of sale or its modification or termination by agreement or any offer, acceptance or other indication of intention to be made in any form other than in writing does not apply where any party has his place of business in a Contracting State which has made a declaration under artiole 96 of this Convention. The parties may not derogate from or vary the effect of this article.
Article 13
For the purposes of this Convention "writing" includes telegram and telex.
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