Some properties of line digraphs

@article{Harary1960SomePO,
  title={Some properties of line digraphs},
  author={F. Harary and R. Z. Norman},
  journal={Rendiconti del Circolo Matematico di Palermo},
  year={1960},
  volume={9},
  pages={161-168}
}
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Our object is to find a generating function whose coefficients give the number of isomorphism types of functional digraphs with a given finite number of points. I t will be seen that functionalExpand
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