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Charles Read
University of Leeds
NONSTANDARD IDEALS; MARC THOMAS AS FATHER OF
ALL COUNTEREXAMPLES; APPLICATIONS TO OPERATOR
ALGEBRAS
Monday, March 19, 2012 3pm, 646 PGH
Abstract
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Pretty much the prototypic commutative Banach algebra is the convolution algebra l_1. As befits a semisimple
commutative Banach algebra, l_1 has very many closed ideals. But if one imposes a radical weight - considering the
radical convolution algebra l_1(w) for a radical weight w
- the only obvious or “standard” ideals are the ideals J_n consisting
of functions supported on the interval [n,1). It is a beautiful result of
Marc Thomas, however, that nonstandard ideals exist, for certain choices of the weight w. This pioneering example has been
modified for various purposes by Read, Dales et al. But if the weight is well behaved, all the ideals are standard. The
best general result in this direction is by Domar. This good behaviour sometimes spills over from the l_1 situation to
that of some closely related operator algebras; a fact used in the recent collaboration of Blecher and Read.
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