Abstract
Aguiar and Ardila defined the Hopf monoid ${\rm GP}$ of generalized permutahedra and showed that it contains many submonoids that correspond to combinatorial objects. They also give a basic polynomial invariant of generalized permutahedra, which then specializes to submonoids. We define the Hopf monoid of directed graphs and show that it also embeds in ${\rm GP}$. The resulting basic invariant coincides with the strict chromatic polynomial of Awan and Bernardi.
Acknowledgments
I should like to express my gratitude to Tamás Kálmán for constant encouragement and much helpful advice. I should also like to thank Keita Nakagane for his useful comments and discussions.
Citation
Keiju Kato. "The Hopf monoid and the basic invariant of directed graphs." Osaka J. Math. 58 (3) 591 - 608, July 2021.
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