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From noncommutative diagrams to anti-elementary classes

    https://doi.org/10.1142/S0219061321500112Cited by:5 (Source: Crossref)

    Anti-elementarity is a strong way of ensuring that a class of structures, in a given first-order language, is not closed under elementary equivalence with respect to any infinitary language of the form λ. We prove that many naturally defined classes are anti-elementary, including the following:

    • the class of all lattices of finitely generated convex -subgroups of members of any class of -groups containing all Archimedean -groups;

    • the class of all semilattices of finitely generated -ideals of members of any nontrivial quasivariety of -groups;

    • the class of all Stone duals of spectra of MV-algebras — this yields a negative solution to the MV-spectrum Problem;

    • the class of all semilattices of finitely generated two-sided ideals of rings;

    • the class of all semilattices of finitely generated submodules of modules;

    • the class of all monoids encoding the nonstable K0-theory of von Neumann regular rings, respectively, C*-algebras of real rank zero;

    • (assuming arbitrarily large Erdős cardinals) the class of all coordinatizable sectionally complemented modular lattices with a large 4-frame.

    The main underlying principle is that under quite general conditions, for a functor Φ:𝒜, if there exists a noncommutative diagram D of 𝒜, indexed by a common sort of poset called an almost join-semilattice, such that

    • ΦDI is a commutative diagram for every set I,

    • ΦD for any commutative diagram X in 𝒜,

    then the range of Φ is anti-elementary.

    AMSC: 18A30, 18A35, 03E05, 06A07, 06A12, 06C20, 06D22, 06D35, 06F20, 08C05, 08A30, 16E20, 16E50