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Article . 1964
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Transactions of the American Mathematical Society
Article . 1964 . Peer-reviewed
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Transactions of the American Mathematical Society
Article . 1964 . Peer-reviewed
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Some Uncomplemented Function Algebras

Some uncomplemented function algebras
Authors: Glicksberg, I.;

Some Uncomplemented Function Algebras

Abstract

1. Let X be the unit circle Iz I = 1, and A the "disc algebra" of functions on X having continuous extensions to I z ? < 1 analytic for I z I < 1. Then it is known [12] that there is no bounded projection of C(X) onto A; alternatively, A is uncomplemented in C(X). To what extent is this a general occurrence? Specifically, if A is a closed nonselfadjoint(2) subalgebra of C(X), X compact, is A uncomplemented in C(X)? Only some partial results will emerge here. From recent results of Bishop [1], extended to the nonmetric case by Bishop and deLeeuw in [2], we obtain the curious fact that if X is the Silov boundary of A, and T is any bounded operator on C(X) acting as the identity on A, then T I || = 11 T |1, where I is the identity operator; alternatively, any operator S (= I T) annihilating A has || I + S || = 1 + || S ||. As a consequence of this fact one can apply the technique of [12] to show that if X is a compact group and our nonselfadjoint subalgebra A of C(X) is translation invariant, A is uncomplemented; in fact any closed subspace lying between two invariant algebras A1 c A2, with the set of conjugates A1 t A2, is uncomplemented (?3). And this applies equally well to invariant subalgebras A1, A2 of(3) CO(X), where X is a locally compact abelian group (?4); but both proofs are technically complicated, and shed no light on the situation in general. In what follows we shall consider a slightly more general setting in which A is a subalgebra of CO(X), X locally compact; since we shall be concerned with estimating the norms of projections, the usual adj unction of an identity does not lead easily to a reduction to the compact case. The author is indebted to K. deLeeuw for several helpful comments and, in particular, Theorem 4.1 is due to deLeeuw.

Keywords

functional analysis

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
9
Average
Top 10%
Average
bronze