The generalized degree-of-satisfiability conjecture for reasonable measures

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

ds⁡(G,E,{μn}n∈N)=lim sup⁡n→∞μn×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}n∈N)\operatorname{dc}(G,\{\mu_n\}_{n\in\mathbb{N}}) for this degree. Generalized degree-of-satisfiability conjecture. Then

ds⁡(G,E,{μn}n∈N)>0⟺E 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}n∈N)>0⟺G 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.

References

Primary source

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

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