A counterexample to the reconstruction of $\omega$-categorical structures from their endomorphism monoids
Abstract
We present an example of two countable -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 -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