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317 Boolean Analysis — General

317.1 Overview

Increasing symmetric Boolean functions and graph properties admit quantitative threshold and approximation statements. Structural statements for finite products describe boosters, pseudo-juntas, and input-dependent notable coordinates.

317.2 Declarations

Theorem 317.1 Narrow thresholds for transitive Boolean functions
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There exists an absolute \(B\gt 0\) such that for every \(n\ge 2\), nonconstant increasing transitively symmetric \(f:\{ 0,1\} ^n\to \{ 0,1\} \), \(0\lt p_c\le 1/2\) with \(\Pr _{p_c}(f=1)=1/2\), and \(0\lt \varepsilon \lt 1/4\), the number \(\eta =B\log (1/\varepsilon )\log (1/p_c)/\log n\) satisfies: if \(\eta \le 1/2\), then \(\Pr _{p_c(1-\eta )}(f=1)\le \varepsilon \) and \(\Pr _{p_c(1+\eta )}(f=1)\ge 1-\varepsilon \).

Theorem 317.2 Graph sharp-threshold approximation
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There exists \(w:\mathbb R\times \mathbb R\to \mathbb N\) such that whenever the \(n\) variables bijectively index the edges of a labeled simple graph on \(v\) vertices, \(f:\{ 0,1\} ^n\to \{ 0,1\} \) is an increasing graph property, \(0\lt p\le 1/2\), \(K\gt 0\), \(0\lt \varepsilon \lt 1\), and \(I_p(f)\le K\), there is a monotone DNF \(d\) of width at most \(w(K,\varepsilon )\) with \(\Pr _p(f\ne d)\le \varepsilon \). Here \(I_p(f)=4p(1-p)\) times the sum of pivotal probabilities.

Theorem 317.3 Bourgain booster theorem
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There are absolute \(C,D\gt 0\) such that for every product \(P\) of \(n\) finite probability spaces with strictly positive atom masses and outcome space \(\Omega =\prod _i\Omega _i\), every \(f:\Omega \to \{ -1,1\} \), and every real \(K\) satisfying \(I(f)\le K\) and \(\operatorname {Var}_P(f)\ge 1/100\), there exists \(\tau \in \mathbb R\) with \(e^{-CK^2}\le |\tau |\le \Pr _P(\exists T\subseteq [n],\ |T|\le DK:\ (T,x)\text{ is a }\tau \text{-booster})\). A \(\tau \)-booster has \(E_Tf(x)\ge \mathbb E_Pf+\tau \) for \(\tau \gt 0\), or \(E_Tf(x)\le \mathbb E_Pf+\tau \) for \(\tau \lt 0\).

Theorem 317.4 Hatami pseudo-junta approximation
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There is an absolute \(C\gt 0\) such that for every product \(P\) of \(n\) finite probability spaces with strictly positive atom masses and outcome space \(\Omega =\prod _i\Omega _i\), every \(f:\Omega \to \{ -1,1\} \), \(K\ge 0\) with \(I(f)\le K\), and \(\varepsilon \gt 0\), there is \(h:\Omega \to \{ -1,1\} \) with \(\Pr _P(f\ne h)\le \varepsilon \) that is determined by locally triggered coordinate observations exposing at most \(\exp (CK^3/\varepsilon ^3)\) coordinates in expectation.

Theorem 317.5 Influence of Boolean pseudo-juntas
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Let \(P\) be a product of \(n\) finite probability spaces with strictly positive atom masses and outcome space \(\Omega =\prod _i\Omega _i\), \(h:\Omega \to \{ -1,1\} \), and \(K\in \mathbb R\). If \(h\) is determined by locally triggered coordinate observations whose expected exposed size is at most \(K\), with each trigger depending only on its declared coordinate set, then \(I(h)\le 4K\).

Theorem 317.6 Bourgain notable-coordinate structure
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There are absolute \(C,D\gt 0\) such that for every product \(P\) of \(n\) finite probability spaces with strictly positive atom masses and outcome space \(\Omega =\prod _i\Omega _i\), every \(f:\Omega \to \{ -1,1\} \), and \(0\lt \varepsilon \lt 1/2\), putting \(k=I(f)/\varepsilon \), there exist sets \(J(x)\subseteq [n]\) satisfying \(|J(x)|\le e^{Ck}\) and \(|\{ S\subseteq J(x):|S|\le k\} |\le e^{Dk^2}\) for every \(x\), and \(\mathbb E_P\sum _{S\notin \{ T\subseteq J(x):|T|\le k\} }f_S(x)^2\le 2\varepsilon \).

Theorem 317.7 Nonnotable randomized Laplacian estimate
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Let \(P\) be a product of \(n\) finite probability spaces with strictly positive atom masses and outcome space \(\Omega =\prod _i\Omega _i\), \(f:\Omega \to \mathbb R\), \(x\in \Omega \), a coordinate \(i\), and \(\tau \gt 0\). If \(\sum _{S\ni i}f_S(x)^2\lt \tau \), put \(g=T_{2/5}L_if\) and \(h(r)=\sum _S\chi _S(r)g_S(x)\); then on the uniform sign cube \(\| T_{1/\sqrt3}h\| _2^2\le \tau ^{1/3}\| h\| _{4/3}^{4/3}\).