An ordered set is a container of variable length with two special requirements to the elements: all possible element values are comparable and build a total ordering; the elements of a set follow in a strictly ascending order, which also implies that all elements are different. This notion of a set is identical to that from the STL; the differences are primarily in the implementation details.

You can choose between two persistent set classes:

There are also various constructions representing sets of subsets, so called power sets: