Having derived a number of main aggregates, both positional and non-positional, we can now more clearly define the very concept of such. We call the main set one that can be completely and unambiguously deduced from a given number of elements, if all these elements play the same role in the construction. If we designate these elements by letters and derive the construction of a collection, introducing first the elements marked with certain letters and then with the other ones, then, if the deduced collection is the main one, we can move the letters in relation to the elements differently, and the construction remains valid if in its order during the course of the process, we kept the original letters.
