Exercises for the Pcmi Summer School

نویسنده

  • EMMANUEL BREUILLARD
چکیده

2) Suppose that Γ is a 4-paradoxical group and Γ = A1∪A2∪B1∪B2 is a paradoxical decomposition as defined above. Show that Γ plays ping-pong on itself, where the pingpong players are a := a−1 1 a2 and b := b −1 1 b2 .Deduce that Γ contains a non-abelian free subgroup F2. 3) Define the Tarski number T (Γ) of a group Γ to be the smallest integer N if it exists such that Γ is N -paradoxical. By the above T (Γ) = 4 if and only if Γ contains F2. Show that if Γ is amenable, then T (Γ) = +∞.

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تاریخ انتشار 2012