Functions built from intersections of set families satisfy a strong hypergraph regularity lemma, and the two known sources of ternary instability both satisfy this regularity, so strong 2-stability cannot be defined by excluded hypergraphs.
Intersecting sets in probability spaces and Shelah's classification
1 Pith paper cite this work. Polarity classification is still indexing.
abstract
For $n \in \mathbb{N}$ and $\varepsilon > 0$, given a sufficiently long sequence of events in a probability space all of measure at least $\varepsilon$, some $n$ of them will have a common intersection. A more subtle pattern: for any $0 < p < q < 1$, we cannot find events $A_i$ and $B_i$ so that $\mu \left( A_i \cap B_j \right) \leq p$ and $\mu \left( A_j \cap B_i\right) \geq q$ for all $1 < i < j < n$, assuming $n$ is sufficiently large. This is closely connected to model-theoretic stability of probability algebras. We survey some results from our recent work on more complicated patterns that arise when our events are indexed by multiple indices. In particular, how such results are connected to higher arity generalizations of de Finetti's theorem in probability, structural Ramsey theory, hypergraph regularity in combinatorics, and model theory.
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Averages of hypergraphs and higher arity stability
Functions built from intersections of set families satisfy a strong hypergraph regularity lemma, and the two known sources of ternary instability both satisfy this regularity, so strong 2-stability cannot be defined by excluded hypergraphs.