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Dec 4, 2011 at 21:08 comment added Yemon Choi It may be worth remarking that a notorious open question in Banach algebras asks: does there exist an infinite-dimensional commutative Banach algebra (necessarily non-unital and radical) which is algebraically simple? The question has been open since the 1970s (I think).
Dec 4, 2011 at 16:48 comment added Bill Johnson Right, Sellapan. There are many Banach algebras that have a largest (necessarily closed) ideal which you can mod out to get an example.
Dec 4, 2011 at 16:03 answer added Alain Valette timeline score: 9
Dec 4, 2011 at 13:56 history edited Sellapan Nathan CC BY-SA 3.0
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Dec 4, 2011 at 13:53 comment added Sellapan Nathan Perhaps the Calkin algebrea $B(H)/K(H)$ is a good candidate.
Dec 4, 2011 at 13:43 comment added Sergei Akbarov Besides this, do you mean algebras with identity?
Dec 4, 2011 at 13:41 comment added Sergei Akbarov Yes, the ideal $F(H)$ of all finite-dimensional operators in $K(H)$ is non-trivial. But as far as I understand, if you don't claim that $J$ is closed, then $K(H)$ is not a counterexample for you. I.e. $K(H)$ is not algebraically simple...
Dec 4, 2011 at 13:34 comment added Johannes Hahn @Sergei: I think, that's exactly the point: is this algebraically simple. In other words: Are there non-closed two-sided ideals other than {0} and the whole algebra??
Dec 4, 2011 at 13:33 comment added Sergei Akbarov Will the algebra $K(H)$ of compact operators on a Hilbet space satisfy you? It has not non-trivial (closed) two-sided ideals.
Dec 4, 2011 at 13:20 history edited Sellapan Nathan
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Dec 4, 2011 at 13:09 history asked Sellapan Nathan CC BY-SA 3.0