... bipartite digraphs, namely, specifying conditions on thecardinality of the edge-set of the digraph that guarantee the existence of a directed simplecycle of length at most four. As usual in Tur´an ... ,m and j = ρn +1, ,2ρn.DenotethisblockM2.DenotebyM3the block consisting of the rows i = |A+|+1, ,m and the columnsj =1, ,ρn.DenotebyM4the block consisting of the rows i = |A+|+1, ... ,n.DenotebyM5the block consisting of the rows i =1, ,|A+|and the columns j =2ρn +1, ,n. Define β = |A+|/m. Figure 1 visualizes these terms.Let c(s, k) denote the number of entries of M...