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Tsung-Hsuan Tsai

Freiheitssatz for the density model of random groups
Vendredi, 17 Décembre, 2021 - 10:30
Résumé : 

Magnus' Freiheitssatz states that if a group is defined by a presentation with $m$ generators and a single cyclically reduced relator, and this relator contains the last generating letter, then the first $m-1$ letters freely generate a free subgroup. We study an analogue of this theorem in the Gromov density model of random groups, showing a phase transition phenomenon at density $d_r = \min\{\frac{1}{2}, 1-\log_{2m-1}(2r-1)\}$ with $1\leq r\leq m-1$: we prove that for a random group with $m$ generators at density $d$, if $d<d_r$ then the first $r$ letters freely generate a free subgroup; whereas if $d>d_r$ then the first $r$ letters generate the whole group.

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