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arxiv: 0812.2888 · v1 · pith:NMAFHXGUnew · submitted 2008-12-15 · 🧮 math.GN · math.GR

Super-sequences in the arc component of a compact connected group

classification 🧮 math.GN math.GR
keywords compactgroupconnectedabeliancomponentinfiniteonlysuper-sequence
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Let G be an abelian topological group. The symbol \hat{G} denotes the group of all continuous characters \chi : G --> T endowed with the compact open topology. A subset E of G is said to be qc-dense in G provided that \chi(E) \subseteq \phi([-1/4,1/4]) holds only for the trivial character \chi \in \hat{G}, where \phi : R --> T = R/Z is the canonical homomorphism. A super-sequence is a non-empty compact Hausdorff space S with at most one non-isolated point (to which S converges). We prove that an infinite compact abelian group G is connected if and only if its arc component G_a contains a super-sequence converging to 0 that is qc-dense in G. This gives as a corollary a recent theorem of Aussenhofer: For a connected locally compact abelian group G, the restriction homomorphism r : \hat{G} --> \hat{G}_a defined by r(\chi) = \chi\restriction_{G_a} for \chi \in \hat{G}, is a topological isomorphism. We also show that an infinite compact group G is connected if and only if its arc component G_a contains a super-sequence S converging to the identity e that generates a dense subgroup of G (equivalently, S \setminus {e} is an infinite suitable set for G in the sense of Hofmann and Morris).

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