“…If a vertex x i of D is a source (i.e., has only arrows leaving x i ) we shall always assume d i = 1 because in this case the definition of I(D) does not depend on the weight of x i . In the special case when d i = 1 for all i, we recover the edge ideal of the graph G which has been extensively studied in the literature [8,11,14,18,20,30,38,39,40,42]. A vertex-weighted digraph D is called Cohen-Macaulay (over the field K) if R/I(D) is a Cohen-Macaulay ring.…”