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DESCRIPTION:TITRE / TITLE\n\nCorona Rigidity\n	\n	RÉSUMÉ / ABSTRACT\n\nThis s
 tory started with Weyl’s work on compact perturbations of pseudo-different
 ial operators. The Weyl-von Neumann theorem asserts that two self-adjoint 
 operators on a complex Hilbert space are unitarily equivalent modulo compa
 ct perturbations if and only if their essential spectra coincide. This was
  extended to normal operators by Berg and Sikonia. New impetus was given i
 n the work of Brown\, Douglas\, and Fillmore\, who replaced single operato
 rs with (separable) C*-algebras and compact perturbations with extensions 
 by the ideal of compact operators. After passing to the quotient (the Calk
 in algebra\, Q) and identifying an extension with a *-homomorhism into Q\,
  analytic methods have to be supplemented with methods from algebraic topo
 logy\, homological algebra\, and (most recently) logic. Some attention wil
 l be given to the (still half-open) question of Brown-Douglas-Fillmore\, w
 hether Q has an automorphism that flips the Fredholm index. It is related 
 to a very general question about isomorphisms of quotients\, asking under 
 what additional assumptions such isomorphism can be lifted to a morphism b
 etween the underlying structures. As general as it is\, many natural insta
 nces of this question have surprisingly precise (and surprising) answers. 
 This talk will be partially based on the preprint Farah\, I.\, Ghasemi\, S
 .\, Vaccaro\, A.\, and Vignati\, A. (2022). Corona rigidity. arXiv preprin
 t arXiv:2201.11618 https://arxiv.org/abs/2201.11618 and some more recent r
 esults.\n	 \n\nZOOM\n	https://us06web.zoom.us/j/84226701306?pwd=UEZ5NVpZaUll
 dW5qNU8vZzIvbEJXQT09\n
DTSTART:20240301T203000Z
DTEND:20240301T213000Z
SUMMARY:Ilijas Farah (York University)
URL:/mathstat/channels/event/ilijas-farah-york-univers
 ity-355701
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