the subject ma er, or the agreement is unclear, the seller has no right to request the buyer to pay such fee. Ar cle 640 The risks of destruc on, damage, or loss of the subject ma er shall be borne by the seller within the period for the trial use. Ar cle 641 The par es may agree in a sales contract that the seller retains the ownership of the subject ma er if the buyer fails to pay the price or perform other obliga ons. The ownership of the subject ma er retained by a seller, without being registered, shall not be asserted against a bona de third. Ar cle 642 Where the par es agree that the seller shall retain the ownership of the subject ma er of the contract, unless otherwise agreed by the par es, the seller has the right to take back the subject ma er if the buyer falls under any of the following circumstances before such ownership is transferred and losses are thus caused to the seller: (1) the buyer fails to make payment in accordance with the contract, and fails to pay it within a reasonable period of me a er being demanded; (2) the buyer fails to ful ll the speci c condi ons in accordance with the contract; or (3) the buyer sells, pledges, or otherwise improperly disposes of the subject ma er. The seller may nego ate with the buyer to take back the subject ma er. Where such nego a on fails, the procedures for enforcement of security interests may be applied muta s mutandis. Ar cle 643 A er a seller has taken back the subject ma er according to the rst paragraph of the preceding Ar cle, the buyer may request to redeem the subject ma er if he eliminates the cause for the seller’s retrieving of the subject ma er within a reasonable period of redemp on agreed by the par es or set by the seller. Where a buyer does not redeem the subject ma er within the redemp on period, the seller may sell the subject ma er to a third person at a reasonable price. A er deduc ng from the sale proceeds the amount unpaid by the buyer and the necessary expenses, any balance shall be returned to the buyer; if the sale proceeds are insu cient to cover the unpaid amount and the other necessary expenses, the de ciency shall be paid by the buyer. Ar cle 644 The rights and obliga ons of the par es to a sale through bidding, as well as the procedures for the bidding, shall be governed by the provisions of the relevant laws and administra ve regula ons. Ar cle 645 The rights and obliga ons of the par es to an auc on, as well as the procedures of the auc on, shall be governed by the provisions of the relevant laws and administra ve regula ons. Ar cle 646 Where there are provisions of laws governing other non-gratuitous contracts, such provisions shall be followed. In an absence of such a provision, the relevant provisions on sales contracts shall be applied muta s mutandis. Ar cle 647 Where the par es agree to transfer the ownership of the subject ma er by barter trade, the relevant provisions on sales contracts shall be applied muta s mutandis. Chapter X Contracts for the Supply and Consump on of Electricity, Water, Gas, or Heat Ar cle 648 A contract for the supply and consump on of electricity is a contract under which a supplier provides electricity to the consumer who pays the price in return. A supplier providing electricity to the public shall not refuse a reasonable request of a consumer to conclude a contract. Ar cle 649 A contract for the supply and consump on of electricity generally contains clauses specifying the mode, quality and me of the supply, the volume, address, and nature of the consump on, the measuring ti tt fi tt ti ti ti ti ti ti ti tt tt fi ti ti ti tt ti tt ti ti ti ti tt ft tt ti ti ti tt ti ti ti ti fi tt ti ti ti tt ti ti fi ti ti ti ffi ft tt fi ft ti tt ti tt ti ti ti ti ti ti ti ti ti ti ti 71