Cameron's Cofinitary Group Conjecture
β 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.
β¦ Synopsis
Recall that S or Sym β«ήβ¬ is the topological group consisting of all Ο± w x permutations of β«ήβ¬ 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 β«,ήβ¬ 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 β«.ήβ¬ 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 β«.ήβ¬ A subΟ± group G -S is cofinitary if for all g g G Ο± α Ο± n g β«ήβ¬ g n s n Β« αn g β«ήβ¬ g n s n ;
π SIMILAR VOLUMES
Let D be a division ring (possibly commutative) and V an infinite-dimensional left vector space over D. We consider irreducible subgroups G of GL(VJ containing an element whose fixedpoint set in V is non-zero but finite dimensional (over D). We then derive conclusions about cofinitary groups, an ele
On a Conjecture of Cameron and Liebler ## KELDON DRUDGE Cameron-Liebler line classes arose from an attempt by Cameron and Liebler to classify those collineation groups of PG(n, q) which have the same number of orbits on points as on lines. They satisfy several equivalent properties; among them, c
We prove that every maximal cofinitary group has size at least the cardinality of the smallest non-meager set of reals. We also provide a consistency result saying that the spectrum of possible cardinalities of maximal cofinitary groups may be quite arbitrary.