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Maximal Digraphs With Respect to Primitive Positive Constructibility

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 نشر من قبل Florian Starke
 تاريخ النشر 2021
  مجال البحث
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We study the class of all finite directed graphs up to primitive positive constructability. The resulting order has a unique greatest element, namely the graph $P_1$ with one vertex and no edges. The graph $P_1$ has a unique greatest lower bound, namely the graph $P_2$ with two vertices and one directed edge. Our main result is a complete description of the greatest lower bounds of $P_2$; we call these graphs submaximal. We show that every graph that is not equivalent to $P_1$ and $P_2$ is below one of the submaximal graphs.



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