(2) A party who has performed the contract either wholly or in part may claim restitution from the other party of whatever the first party has supplied or paid under the contract. If both parties are bound to make restitution, they must do so concurrently.
(1) The buyer loses the right to declare the contract avoided or to require the seller to deliver substitute goods if it is impossible for him to make restitution of the goods substantially in the condition in which he received them.
(2) The preceding paragraph does not apply:
(a) if the impossibility of making restitution of the goods or of making restitution of the goods substantially in the condition in which the buyer received them is not due to his act or omission;
(b) if the goods or part of the goods have perished or deteriorated as a result of the examination provided for in article 38; or
(c) if the goods or part of the goods have been sold in the normal course of business or have been consumed or transformed by the buyer in the course of normal use before he discovered or ought to have discovered the lack of conformity.
A buyer who has lost the right to declare the contract avoided or to require the seller to deliver substitute goods in accordance with article 82 retains all other remedies under the contract and this Convention.
(1) If the seller is bound to refund the price, he must also pay interest on it, from the date on which the price was paid.
(2) The buyer must account to the seller for all benefits which he has derived from the goods or part of them:
(a) if he must make restitution of the goods or part of them; or
(b) if it is impossible for him to make restitution of all or part of the goods or to make restitution of all or part of the goods substantially in the condition in which he received them, but he has nevertheless declared the contract avoided or required the seller to deliver substitute goods.
Section VI. Preservation of the goods
If the buyer is in delay in taking delivery of the goods or, where payment of the price and delivery of the goods are to be made concurrently, if he fails to pay the price, and the seller is either in possession of the goods or otherwise able to control their disposition, the seller must take such steps as are reasonable in the circumstances to preserve them. He is entitled to retain them until he has been reimbursed his reasonable expenses by the buyer.