Von Neumann Conjecture

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Let $G$ be a group.

Then $G$ is non-amenable if and only if $G$ contains a free subgroup of rank $2$.


This conjecture was answered in the negative, by Aleksandr Yuryevich Olshansky.

He demonstrated that the Tarski monster is a non-amenable group with no such free subgroup.

Also see

Source of Name

This entry was named for John von Neumann.