The generalized degree-of-satisfiability conjecture for reasonable measures

Let GG be a group, let {μn}nN\{\mu_n\}_{n\in \mathbb{N}} be a sequence of “reasonable” measures on GG, and let EFk\mathcal{E}\subseteq F_k be a set of equations in kk variables. The degree of satisfiability is

ds(G,E,{μn}nN)=lim supnμn×k({(g1,,gk)Gk:(g1,,gk) is a solution of E}).\operatorname{ds}(G,\mathcal{E},\{\mu_n\}_{n\in \mathbb{N}})=\limsup_{n\to\infty}\mu_n^{\times k}\big(\{(g_1,\ldots,g_k)\in G^k:(g_1,\ldots,g_k)\text{ is a solution of }\mathcal{E}\}\big).

For the commutativity equation, write dc(G,{μn}nN)\operatorname{dc}(G,\{\mu_n\}_{n\in\mathbb{N}}) for this degree. Generalized degree-of-satisfiability conjecture. Then

ds(G,E,{μn}nN)>0E is a virtual law in G.\operatorname{ds}(G,\mathcal{E},\{\mu_n\}_{n\in\mathbb{N}})>0\quad\Longleftrightarrow\quad\mathcal{E}\text{ is a virtual law in }G.

In particular,

dc(G,{μn}nN)>0G is virtually abelian.\operatorname{dc}(G,\{\mu_n\}_{n\in\mathbb{N}})>0\quad\Longleftrightarrow\quad G\text{ is virtually abelian}.

The conjecture proposes that positive asymptotic satisfaction probability is equivalent to an algebraic finite-index law, for suitable measure sequences. The meaning of “reasonable” measures is left informal in the source, so the precise scope and validity of the assertion remain open.

Sources & referencesView supporting material

Primary source

Yago Antolín, Armando Martino and Enric Ventura, “Degree of commutativity of infinite groups”, arXiv:1511.07269 (2015).

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