The appellants were lessees of a flat owned by the respondent. They sought to purchase the property and sent the respondent an unsigned, incomplete written offer on a standard sale of immovable property form, leaving blank the names of the purchasers and the description of the property. The respondent altered the purchase price, inserted her name as seller, signed the document and returned it. Thereafter, the appellants inserted the property description, added their names as purchasers, and signed the document without returning it to the respondent for re-signature. When the respondent later refused to proceed with transfer, the appellants sought to enforce the agreement.