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 d eclaration under article 96 of this Convention. The parties may not derogate from or vary the effect or this article Article 13 PART II FORMATION OF THE CONTRACT Article 14 (1)A proposal for concluding a contract addressed to one or more specif ic persons constitutes an offer if it is suffic iently definite and indicates the intention of the offeror to be bound in case of accep tance. a proposal is sufficientI definite if it indicates the goods and expressly or impl icitly fixes or makes provision for deter mining the quantity a nd the price. (2)A proposal other than one addressed to one or more spec ific persons is to be considered merely as an invitation to make offers, unless the contrary is clearly indicated by the person making the proposal (1)An offer becomes effective when it reaches the offeree (2)An offer, even if it is irrevocable, may be withdrawn if the withdrawal reaches the offeree before or at the same ne as the offer. Article 16 (1)Until a contract is concluded an offer may be revoked if the revocation reaches the offeree before he has dispat (2)However, an offer cannot be revoked: (a)if it indicates, whether by stating a fixed time for acceptance or otherwise, that it is irrevocable, or (b) if it was reasonable for the offeree to rely on the offer as being irrevocable and the offeree has acted in reliance Article 17 An offer, even if it is irrevocable, is terminated when a rejection reaches the offeror. Article 18 四 by or other conduct of the offeree indicating assent to an offer is an acceptance. Silence or in (2)An acceptance of an offer becomes effective at the moment the indication of assent reaches the offeror. An acce ptance is not effective if the indication of assent does not reach the offeror with in the time he has fixed or, if no tim e is fixed with in a reasonable time, due account being taken of the circumstan ces of the transaction, including th rapidity of the means of communication employed by the offeror. An oral offer must be accepted immediately unle ss the circumstances indicate otherwise (3)However, if, by virtue of the offer or as a result of practices which the parties have established between themsel ves or of usage, the offeree may indicate assent by performing an act, such a ating to the dispatch of the ods or payment of the price, without notice to the offeror, the acceptance is effective at the moment the act is perfo med, provided that the act is performed within the period of time laid down in the preceding paragraph (1)A reply to an offer which purports to be an acceptance but contains add itions, limitations or other modifications is a rejection of the offer and constitutes a counter-o (2)However, a reply to an offer which purports to be an acceptance but contains additional or different terms whi h do not materially alter the terms of the offer constitutes an acceptance, unless the offeror, without undue delay, o bjects orally to the discrepancy or dispatches a notice to that effect. If he does not so object, the terms of the contraor 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 d eclaration under article 96 of this Convention. The parties may not derogate from or vary the effect or this article. Article 13 For the purposes of this Convention "writing" includes telegram and telex. PART II FORMATION OF THECONTRACT Article 14 (1) A proposal for concluding a contract addressed to one or more specific persons constitutes an offer if it is suffic iently definite and indicates the intention of the offeror to be bound in case of acceptance. A proposal is sufficiently definite if it indicates the goods and expressly or implicitly fixes or makes provision for determining the quantity a nd the price. (2) A proposal other than one addressed to one or more specific persons is to be considered merely as an invitation to make offers, unless the contrary is clearly indicated by the person making the proposal. Article 15 (1) An offer becomes effective when it reaches the offeree. (2) An offer, even if it is irrevocable, may be withdrawn if the withdrawal reaches the offeree before or at the same time as the offer. Article 16 (1) Until a contract is concluded an offer may be revoked if the revocation reaches the offeree before he has dispat ched an acceptance. (2) However, an offer cannot be revoked: (a) if it indicates, whether by stating a fixed time for acceptance or otherwise, that it is irrevocable; or (b) if it was reasonable for the offeree to rely on the offer as being irrevocable and the offeree has acted in reliance on the offer. Article 17 An offer, even if it is irrevocable, is terminated when a rejection reaches the offeror. Article 18 (1) A statement made by or other conduct of the offeree indicating assent to an offer is an acceptance. Silence or in activity does not in itself amount to acceptance. (2) An acceptance of an offer becomes effective at the moment the indication of assent reaches the offeror. An acce ptance is not effective if the indication of assent does not reach the offeror within the time he has fixed or, if no tim e is fixed, within a reasonable time, due account being taken of the circumstances of the transaction, including the rapidity of the means of communication employed by the offeror. An oral offer must be accepted immediately unle ssthe circumstances indicate otherwise. (3) However, if, by virtue of the offer or as a result of practices which the parties have established between themsel ves or of usage, the offeree may indicate assent by performing an act, such as one relating to the dispatch of the go ods or payment of the price, without notice to the offeror, the acceptance is effective at the moment the act is perfo rmed, provided that the act is performed within the period of time laid down in the preceding paragraph. Article 19 (1) A reply to an offer which purports to be an acceptance but contains additions, limitations or other modifications is a rejection of the offer and constitutes a counter-offer. (2) However, a reply to an offer which purports to be an acceptance but contains additional or different terms whic h do not materially alter the terms of the offer constitutes an acceptance, unless the offeror, without undue delay, o bjects orally to the discrepancy or dispatches a notice to that effect. If he does not so object, the terms of the contra