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Hello,

You should merge the vertices "d" and "e". You can do that using the method "merge_vertices" of digraphs.

sage: D = DiGraph()
sage: D.add_edge('a', 'b')
sage: D.add_edge('b', 'c')
sage: D.edges(labels=False)
 [('a', 'b'), ('b', 'c')]
sage: D.merge_vertices(['a', 'c'])
sage: D.edges(labels=False)
[('a', 'b'), ('b', 'a')]

Vincent