A k-subset is a subset of a set on n elements containing exactly k elements. The number of k-subsets on n elements is therefore given by the binomial coefficient (n k). For example, there are (3 2) = 3 2-subsets of {1, 2, 3}, namely {1, 2}, {1, 3}, and {2, 3}. The k-subsets of a list can be enumerated in the Wolfram Language as Subsets[list, {k}].

binomial coefficient | combination | pairwise | permutation | p-system | subset