 Instead of listing every single element, sometimes an ellipsis ("...") is used, if the writer believes that the reader can easily guess what is missing; for example, {1, 2, 3, ..., 100} presumably denotes the set of integers from 1 to 100.Even in this case, however, it is still "possible" to list all the elements, because the set is "finite".Some sets are "infinite"; these sets have more than "n" elements for any integer "n".