 The aforementioned definition does not allow a directed graph to have multiple arrows with the same source and target nodes, but some authors consider a broader definition that allows directed graphs to have such multiple arrows (namely, they allow the arrows set to be a multiset).More specifically, these entities are addressed as directed multigraphs (or multidigraphs).On the other hand, the aforementioned definition allows a directed graph to have loops (that is, arrows that directly connect nodes with themselves), but some authors consider a narrower definition that doesn't allow directed graphs to have loops.