Simplicity of Neretin's group of spheromorphisms
Christophe Kapoudjian (1999)
Annales de l'institut Fourier
Similarity:
Denote by , , the regular tree whose vertices have valence , its boundary. Yu. A. Neretin has proposed a group of transformations of , thought of as a combinatorial analogue of the diffeomorphism group of the circle. We show that is generated by two groups: the group of tree automorphisms, and a Higman-Thompson group . We prove the simplicity of and of a family of its subgroups.