What is the validity of selling a non-shared measure of land or a house when the total measure of the structure is unknown?

Primary text

If the parties agree that the intent was to sell a specific, non-shared measure, the sale is invalid. Furthermore, if they do not know the total number of cubits of the house, the sale is invalid because the whole is unknown, and the parts of land are inherently dissimilar, meaning neither a specific nor a shared portion can be precisely defined.