If article III of the Contract, which deals with the topic of Payment of price for the sale of goods and services, is carefully analysed the following factors emerge very clearly: (a) that the pro notes are not expressed to be payments: in fact, it is in terms stated that the "total contract base price shall be paid by purchaser in lawful money of the USA" (article III A) and surely promissory notes are not "lawful money" of USA: 482 (b) that because the Contract so provides even the pro notes also recite that the principal and interest thereunder are "payable in lawful money of the USA"; (c) that article III A (3) which deals with pro notes provides for payment of the remaining 90% of the price "in accordance with the following Schedule of Payments" and expressly states that "the obligation to make such payments is to be evidenced by four series of purchaser 's unconditional negotiable promissory notes", which clearly shows that the pro notes are not payments but are intended merely to be the evidence of the obligation to pay the price; (d) that though stated to be "unconditional and negotiable" (perhaps so between the drawer and subsequent assignees in case of negotiation), as between the seller and the purchaser these have been made subject to several conditions such as (1) the amounts thereof were payable only on the assumption that deliveries of items of equipment were completed within 15 months of Contract Effective Date and interest at the rate of 6 1/2% was to become 6% on receipt of income tax exemption (article III A(3) (b), (ii) these were to lie in Escrow Arrangement to be released to the seller synchronizing with the stated progress of supply of goods according to certain formulae (article III D).