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2^_0 pairwise non-isomorphic maximal-closed subgroups of Sym(N) via the classification of the reducts of the Henson digraphs
[article]
2015
arXiv
pre-print
Given two structures M and N on the same domain, we say that N is a reduct of M if all ∅-definable relations of N are ∅-definable in M. In this article the reducts of the Henson digraphs are classified. Henson digraphs are homogeneous countable digraphs that omit some set of finite tournaments. As the Henson digraphs are _0-categorical, determining their reducts is equivalent to determining all closed supergroups G< Sym(N) of their automorphism groups. A consequence of the classification is
arXiv:1509.07674v1
fatcat:4ebw7uzecfc6dagqntd62ttovu