Abstract
We establish the hierarchy among twelve equivalence relations (similarities) on the class of relational structures: the equality, the isomorphism, the equimorphism, the full relation, four similarities of structures induced by similarities of their self-embedding monoids and intersections of these equivalence relations. In particular, fixing a language L and a cardinal κ, we consider the interplay between the restrictions of these similarities to the class Mod L (κ) of all L-structures of size κ. It turns out that, concerning the number of different similarities and the shape of the corresponding Hasse diagram, the class of all structures naturally splits into three parts: finite structures, infinite structures of unary languages, and infinite structures of non-unary languages (where all these similarities are different).
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Kurilić, M.S. Different similarities. Arch. Math. Logic 54, 839–859 (2015). https://doi.org/10.1007/s00153-015-0443-x
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DOI: https://doi.org/10.1007/s00153-015-0443-x
Keywords
- Relational structure
- Isomorphic substructure
- Partial order
- Self-embedding monoid
- Isomorphism
- Equimorphism
- Forcing-equivalence