Convergence groups are Fuchsian groups
Convergence groups are Fuchsian groups
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收敛群是 Fuchsian 群
DOI:
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发表时间:
1991
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通讯作者:
David Gabai
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文献类型:
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作者:
David Gabai
A group of homeomorphisms of the circle satisfying the "convergence property" is shown to be the restriction of a discrete group of Mobius transformations of the unit disk. This completes the proof of the Seifert fiber space conjecture and gives a new proof of the Nielson realization problem. A Fuchsian group F is a discrete subgroup of the group of Mobius transformations on the unit disc D in R . F restricts to a subgroup G of Homeo(5') which satisfies the following convergence property [GM]. Given a sequence of distinct elements of G, then there exists x, y e S and a subsequence {f.} such that on S {x, y} f. -• y, f~ -> x uniformly on compact sets. A group G c Homeo(5') with this property is called a convergence group. We announce the following result. The details can be found in [G]. Theorem 1. G is a convergence group if and only if G is conjugate in Homeo(5) to the restriction of a Fuchsian group.* A Seifert fibred space is a compact 3-manifold M which is almost an S bundle over a compact surface, i.e. there exists a projection n : M —• TV such that for each x e N there exists a D neighborhood of x such that n~(D) = D x S and 7t((r, 6X)9 (1, 02)) = (r9pOx + Q62) where p ^ O and p, q are relatively prime and depend on x and 6 e Rmod27t. Corollary 2 (Seifert Fibred Space Conjecture). Let M be a compact, orientable, irreducible {i.e. every smooth embedded S bounds a 3-cell) 3-manifold with infinite nx, then M is a Seifert fibred space if and only if nx(M) contains a cyclic normal subgroup. Received by the editors January 7, 1991 and, in revised form, April 20, 1991. 1980 Mathematics Subject Classification (1985 Revision). Primary 57S25; Secondary 20H10, 57N05, 57N10. Partially supported by NSF Grant DMS-8902343 and a Sloan Foundation Fellowship. *Andrew Casson has also announced, using different methods, a proof of Theorem 1. ©1991 American Mathematical Society 0273-0979/91 $1.00+ $.25 per page 395