On a Counterexample to a Conjecture by Blackadar

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  • Adam Peder Wie Sørensen
Blackadar conjectured that if we have a split short-exact sequence 0→I→A→C→0 where I is semiprojective then A must be semiprojective. Eilers and Katsura have found a counterexample to this conjecture. Presumably Blackadar asked that the extension be split to make it more likely that semiprojectivity of I would imply semiprojectivity of A. But oddly enough, in all the counterexamples of Eilers and Katsura the quotient map from A to A/I≅C is split. We will show how to modify their examples to find a non-semiprojective C∗-algebra B with a semiprojective ideal J such that B∕J is the complex numbers and the quotient map does not split.
Original languageEnglish
Title of host publicationOperator Algebra and Dynamics : Nordforsk Network Closing Conference, Faroe Islands, May 2012
EditorsToke M. Clausen, Søren Eilers, Gunnar Restorff, Sergei Silvestrov
PublisherSpringer
Publication date2013
Pages295-303
ISBN (Print)9783642394584
ISBN (Electronic)9783642394591
DOIs
Publication statusPublished - 2013
SeriesSpringer Proceedings in Mathematics & Statistics
Volume58

ID: 97160488