Root cases of large sets of t-designs
Discrete Mathematics
Handbook of Combinatorial Designs, Second Edition (Discrete Mathematics and Its Applications)
Handbook of Combinatorial Designs, Second Edition (Discrete Mathematics and Its Applications)
Self-complementary two-graphs and almost self-complementary double covers
European Journal of Combinatorics
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In this paper we examine the orders of vertex-transitive self-complementary uniform hypergraphs. In particular, we prove that if there exists a vertex-transitive self-complementary k-uniform hypergraph of order n, where k=2^@? or k=2^@?+1 and n=1(mod2^@?^+^1), then the highest power of any prime dividing n must be congruent to 1 modulo 2^@?^+^1. We show that this necessary condition is also sufficient in many cases-for example, for n a prime power, and for k=3 and n odd-thus generalizing the result on vertex-transitive self-complementary graphs of Rao and Muzychuk. We also give sufficient conditions for the existence of vertex-transitive self-complementary uniform hypergraphs in several other cases. Since vertex-transitive self-complementary uniform hypergraphs are equivalent to a certain kind of large sets of t-designs, the results of the paper imply the corresponding results in design theory.