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arxiv: 0903.3614 · v4 · submitted 2009-03-20 · 🧮 math.LO

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Maximal failures of sequence locality in a.e.c

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classification 🧮 math.LO
keywords kappacardinalregularthetatypesamalgamationequalitymaximal
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We are interested in examples of a.e.c. with amalgamation having some (extreme) behaviour concerning types. Note we deal with k being sequence-local, i.e. local for increasing chains of length a regular cardinal (for types, equality of all restrictions imply equality). . For any cardinal theta>= aleph_0 we construct an a.e.c. with amalgamation k with L.S.T.(k) = theta, |tau_K| = theta such that {kappa : kappa is a regular cardinal and K is not (2^kappa, kappa)-sequence-local} is maximal. In fact we have a direct characterization of this class of cardinals: the regular kappa such that there is no uniform kappa^+-complete ultrafilter. We also prove a similar result to "(2^kappa, kappa)-compact for types".

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  1. Examples of non-tame abstract elementary classes of abelian groups

    math.LO 2026-05 unverdicted novelty 8.0

    Constructs K1, an AEC of torsion-free abelian groups that is not finitely tame but is countably tame, plus families K2(2^μ) that fail tameness below any regular uncountable μ below the first measurable cardinal.