FIG. 28A illustrates an example of a case in which purchase applicants are collected in units of products. In this case, for example, purchase applicants of a product A including an element 100x and an element 100y (portions corresponding to the elements 100x and 100y), a product B including the element 100x and an element 100z (portions corresponding to the elements 100x and 100z), and a product C including the element 100x and an element 100w (portions corresponding to the elements 100x and 100w) are collected individually. In the illustrated example, it is assumed that it is difficult to manufacture the products unless, for example, 1000 purchasers are collected. Then, since the number of purchasers of all of the products is less than 1000, it is difficult to manufacture the products.
