Some sets can be enumerated by means of a natural ordering (such as 1, 2, 3, 4, ... for the set of positive integers), but in other cases it may be necessary to impose a (perhaps arbitrary) ordering. In some contexts, such as enumerative combinatorics, the term "enumeration" is used more in the sense of "counting" – with emphasis on determination of the number of elements that a set contains, rather than the production of an explicit listing of those elements.