Directed bipartite graphs containing every possible pair of directed cycles. (English summary) Ars Combin. 60 (2001), 293–306. Summary: “Let D = (V1, V2; A) be a directed bipartite graph with |V1 |  = |V2 |  = n ≥ 2. Suppose that dD(x) + dD(y)  ≥ 3n for all x ∈ V1 and y ∈ V2. Then, with one exception, D contains two vertex-disjoint directed cycles of lengths 2s and 2t, respectively, for any two positive integers s and t with s + t ≤ n.