Tarski Monster

In the area of modern algebra known as group theory, a Tarski monster group, named for Alfred Tarski, is an infinite group ''G'', such that every proper subgroup ''H'' of ''G'', other than the identity subgroup, is a cyclic group of order a fixed prime number ''p''. A Tarski monster group is necessarily simple. It was shown by Alexander Yu. Olshanskii in 1979 that Tarski groups exist, and that there is a Tarski ''p''-group for every prime ''p'' > 10⁷⁵. They are a source of counterexamples to conjectures in group theory, most importantly to Burnside's problem and the von Neumann conjecture.

Definition

Let $p$ be a fixed prime number. An infinite group $G$ is called a Tarski monster group for $p$ if every nontrivial subgroup (i.e. every subgroup other than 1 and G itself) has $p$ elements.

Properties

* $G$ is necessarily finitely generated. In fact it is generated by every two non-commuting elements.
* $G$ is simple. If $N\trianglelefteq G$ and $U\leq G$ is any subgroup distinct from $N$ the subgroup $NU$ would have $p^2$ elements.
* The construction of Olshanskii shows in fact that there are continuum-many non-isomorphic Tarski Monster groups for each prime $p>10^$.
* Tarski monster groups are examples of non-amenable groups not containing any free subgroups.

References

* A. Yu. Olshanskii, An infinite group with subgroups of prime orders, Math. USSR Izv. 16 (1981), 279–289; translation of Izvestia Akad. Nauk SSSR Ser. Matem. 44 (1980), 309–321.
* A. Yu. Olshanskii, Groups of bounded period with subgroups of prime order, Algebra and Logic 21 (1983), 369–418; translation of Algebra i Logika 21 (1982), 553–618.
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Infinite group theory
P-groups

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