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DISCRETENESS CRITERIA FOR MÖBIUS GROUPS ACTING ON II

Published online by Cambridge University Press:  19 June 2009

LIU-LAN LI
Affiliation:
Department of Mathematics, Hengyang Normal University, Hengyang, Hunan 421008, P.R. China (email: lanlimail2008@yahoo.com.cn)
XIAN-TAO WANG*
Affiliation:
Department of Mathematics, Hunan Normal University Changsha, Hunan 410081, P.R. China (email: xtwang@hunnu.edu.cn)
*
For correspondence; e-mail: xtwang@hunnu.edu.cn
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Abstract

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Jørgensen’s famous inequality gives a necessary condition for a subgroup of PSL(2,ℂ) to be discrete. It is also true that if Jørgensen’s inequality holds for every nonelementary two-generator subgroup, the group is discrete. The sufficient condition has been generalized to many settings. In this paper, we continue the work of Wang, Li and Cao (‘Discreteness criteria for Möbius groups acting on ’, Israel J. Math.150 (2005), 357–368) and find three more (infinite) discreteness criteria for groups acting on ; we also correct a linguistic ambiguity of their Theorem 3.3 where one of the necessary conditions might be vacuously fulfilled. The results of this paper are obtained by using known results regarding two-generator subgroups and a careful analysis of the relation among the fixed point sets of various elements of the group.

Type
Research Article
Copyright
Copyright © Australian Mathematical Publishing Association Inc. 2009

Footnotes

This research was partially supported by the Program for NCET (No. 04-0783), NSF of China (No. 10771059) and Hengyang Normal University (No. 08B06).

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