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Equicontinuity, uniform continuity and sequences in topological groups

✍ Scribed by Jean Pierre Troallic


Publisher
Elsevier Science
Year
1999
Tongue
English
Weight
146 KB
Volume
93
Category
Article
ISSN
0166-8641

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✦ Synopsis


Let G be an almost metrizable topological group (for example, a locally compact group). This paper is concerned with the proof of two principal results. First, the following criterion for equicontinuity is proved: Let X be a union of G Ξ΄ -subsets of G, Y a uniform space and H a set of continuous mappings of X into Y ; then for H to be equicontinuous, it is sufficient (and obviously also necessary) that the sequence ((hn(x), hn(xn))) n∈N be eventually in every entourage of Y for each sequence (hn) n∈N in H, each x ∈ X and each sequence (xn) n∈N in X such that limnβ†’+∞ xn = x. Čoban's theorem on dyadicity is a basic tool in the proof of this result. Let e be the identity element of G; it follows immediately from the above criterion that G has equal left and right uniform structures if (and only if) limnβ†’+∞ anb -1 n = e for all sequences (an) n∈N and (bn) n∈N in G such that limnβ†’+∞ a -1 n bn = e (a well-known property in the case when G is metrizable). The second principal result is the following: Let us suppose that the left and right uniform structures on the almost metrizable topological group G are distinct; then the Banach space UR(G) contains a linear isometric copy L of l ∞ such that inf{ 2l + h | h ∈ U(G)} l for all l ∈ L (and consequently, the quotient Banach space UR(G)/U(G) is nonseparable); moreover, if G is complete, then " " can be replaced by "=" (and consequently, UR(G)/U(G) contains a linear isometric copy of l ∞ ).


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