2-Unstable Configurations
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Model Theory
Stability
Tame Regularity
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Abstract
In the recent decades, stability has become central to the field of model theory. It also has a surprising application in combinatorics. Shelah and Malliaris proved that we can obtain a stronger result in the Szemerédi regularity lemma if we restrict our attention to graphs which are sufficiently stable. Other model theoretic tameness notions have been shown to give similar strengthenings of the regularity lemma. Each of these tameness notions are fundamentally binary: they concern formulas of two variables (or more generally formulas with a bipartition of their free variables). There is a hypergraph analogue to the Szemerédi regularity lemma. As in the graph case, there are a number of ways this regularity lemma can be strengthened. In recent years, Chernikov, Terry, Towsner, and Wolf have been working to establish similar connections in the hypergraph case. For example, Chernikov and Towsner proved that hypergraphs which have bounded VC(k) dimension admit a stronger regularity lemma analogous to the NIP regularity lemma for graphs. Terry and Wolf introduced a number of strengthenings to the hypergraph regularity lemma in the case of 3-graphs, one of these "admitting binary error'" is a candidate definition for ternary stability and is focus of this thesis. Terry and Wolf defined a certain metric structure, called a "special 3-graph" which, if present in a 3-graph, forbids the graph from admitting binary error (just as the half graph forbids stability). In this thesis we define "2-unstable configurations". These are variants of "special 3-graphs" in an infinitary, measured setting. We prove these configurations also forbid binary error.