1. SALES; NATURE OF OBLIGATION OF SELLER AND BUYER; ALTERNATIVE REMEDIES FOR BREACH OF OBLIGATION. — The contract of sale gives rise to reciprocal obligations between seller and buyer, since each party obligations conditions upon those of the other, and the obligations of both are derived from a common origin. It follows that, pursuant to Article 1124 of the Civil Code of 1889 (new 1191 of the new Civil Code), the breach by either party of his obligation entitles the other to a choice of alternative remedies: specific performance or rescission, "with damages in either case." The seller in the present case chose to exact specific performance of the contract in view of the buyer’s defaults in the payment of the price, and demanded the balance thereof. She had the right to do so, unless she had waived such remedy, either in the contract or by subsequent choice on her part.

2. ID.; ID.; ID.; WAIVER OF REMEDY CAN NOT BE PRESUMED. — The sole fact that the contract of sale between the parties only provides that in case of default, "the buyer authorizes the seller to recover her half participation