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Cameron's Cofinitary Group Conjecture

✍ Scribed by Greg Hjorth


Publisher
Elsevier Science
Year
1998
Tongue
English
Weight
160 KB
Volume
200
Category
Article
ISSN
0021-8693

No coin nor oath required. For personal study only.

✦ Synopsis


Recall that S or Sym β€«ήŽβ€¬ is the topological group consisting of all Ο± w x permutations of β€«ήŽβ€¬ equipped with the natural topology. In Ca Cameron defines an element of S to be cofinitary if it fixes only finitely many Ο± elements of ‫,ήŽβ€¬ a subgroup of S to be cofinitary if all its elements other Ο± than the identity are cofinitary, and goes on to conjecture: Ε½ . 0.1. Conjecture Cameron . Every closed cofinitary group is locally compact. If true, this would entail that all subgroups of S arising as continuous Ο± images of closed cofinitary groups are locally compact. In this paper it is shown that Cameron's conjecture is false in the following strong sense: 0.2. THEOREM. EΒ¨ery closed subgroup of S is the continuous homomorΟ± phic image of a closed cofinitary group. 1. SOME DEFINITIONS AND EXAMPLES 1.1. DEFINITION. S , the infinite symmetric group, is the group of all Ο± permutations of ‫.ήŽβ€¬ This group is given the topology generated by all Γ„ Ε½ . 4 subbasic open sets of the form g g S : g n s k for n, k g ‫.ήŽβ€¬ A subΟ± group G -S is cofinitary if for all g g G Ο± ᭚ Ο± n g β€«ήŽβ€¬ g n s n Β« α­™n g β€«ήŽβ€¬ g n s n ;


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