English

A counterexample to the reconstruction of $\omega$-categorical structures from their endomorphism monoids

Logic 2016-07-04 v2

Abstract

We present an example of two countable ω\omega-categorical structures, one of which has a finite relational language, whose endomorphism monoids are isomorphic as abstract monoids, but not as topological monoids -- in other words, no isomorphism between these monoids is a homeomorphism. For the same two structures, the automorphism groups and polymorphism clones are isomorphic, but not topologically isomorphic. In particular, there exists a countable ω\omega-categorical structure in a finite relational language which can neither be reconstructed up to first-order bi-interpretations from its automorphism group, nor up to existential positive bi-interpretations from its endomorphism monoid, nor up to primitive positive bi-interpretations from its polymorphism clone.

Keywords

Cite

@article{arxiv.1510.00356,
  title  = {A counterexample to the reconstruction of $\omega$-categorical structures from their endomorphism monoids},
  author = {Manuel Bodirsky and David Evans and Michael Kompatscher and Michael Pinsker},
  journal= {arXiv preprint arXiv:1510.00356},
  year   = {2016}
}

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17 pages