Stationarity dichotomy conjecture for abstract elementary classes

Let k{\mathfrak k} be an abstract elementary class and define

C0fp={λ:λ=λ and cf(λ)=0}.C^{\rm fp}_{\aleph_0}=\{\lambda:\lambda=\beth_\lambda\text{ and }{\rm cf}(\lambda)=\aleph_0\}.

Set

S1={λC0fp:I˙(λ,k)<λ},S2={λC0fp:I˙(λ,k)λ}.S_1=\{\lambda\in C^{\rm fp}_{\aleph_0}:\dot I(\lambda,\mathfrak k)<\lambda\},\qquad S_2=\{\lambda\in C^{\rm fp}_{\aleph_0}:\dot I(\lambda,\mathfrak k)\geq\lambda\}.

Stationarity dichotomy conjecture. The classes S1S_1 and S2S_2 are not both stationary. A weaker version replaces S2S_2 by the class of λC0fp\lambda\in C^{\rm fp}_{\aleph_0} such that every MKλkM\in K^{\mathfrak k}_\lambda has k\leq_{\mathfrak k}-extensions of every cardinality greater than λ\lambda. The source presents these as conjectures motivated by controlling the categoricity spectrum, with no resolution stated.

Sources & referencesView supporting material

Primary source

Saharon Shelah, “A.E.C. with not too many models”, arXiv:1302.4841 (2013).

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