A -subset is a subset of a set on elements containing exactly elements. The number of -subsets on elements is therefore given by the binomial coefficient . For example, there are 2-subsets of , namely , , and .
The -subsets of a list can be enumerated in the Wolfram Language as Subsets[list, k].
The total number of distinct -subsets on a set of elements (i.e., the number of subsets) is given by