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Approximations of groups, characterizations of sofic groups, and equations over groups. (English) Zbl 1364.20013

Author’s abstract: We give new characterizations of sofic groups:
A group \(G\) is sofic if and only if it is a subgroup of a quotient of a direct product of alternating or symmetric groups.
A group \(G\) is sofic if and only if any system of equations solvable in all alternating groups is solvable over \(G\).
The last characterization allows to express soficity of an existentially closed group by \(\forall\exists \)-sentences.

MSC:

20E26 Residual properties and generalizations; residually finite groups
20E18 Limits, profinite groups
20F70 Algebraic geometry over groups; equations over groups

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