Mark (buyer) and Titius (seller) agreed to sell 10 bags of grain. The grain was measured, piled in the barn of the seller, the keys to which were transferred to the buyer. At night from a lightning strike, the barn and the grain in it burned.
Mark demanded that Titius give him the same amount of grain, Titius refused.
Are there any obligations between Mark and Titius? Did the transfer of ownership from buyer to seller take place? Are the buyer's requirements legitimate?

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