Given two positive integers n and k, the bipartite Kneser graph H(n, k) is the graph whose two bipartite sets of vertices represent the k-subsets and (n - k)-subsets of {1, ..., n} and where two vertices are connected if and only if they are in different sets and one is a subset of the other. H(n, k) therefore has 2(n k) vertices and is regular of degree (n - k k). By definition, H(n, k) is isomorphic to H(n, n - k). H(n, k) is the bipartite double graph of the Kneser graph K(n, k).