Essential spectra of elementary operators
Essential spectra of elementary operators
This paper describes the essential spectrum and index function of the operator <inline-formula content-type="math/mathml"> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="upper X right-arrow upper A upper X upper B"> <mml:semantics> <mml:mrow> <mml:mi>X</mml:mi> <mml:mo stretchy="false">→<!-- → --></mml:mo> <mml:mi>A</mml:mi> <mml:mi>X</mml:mi> <mml:mi>B</mml:mi> </mml:mrow> <mml:annotation encoding="application/x-tex">X \to AXB</mml:annotation> </mml:semantics> </mml:math> </inline-formula>, where <inline-formula content-type="math/mathml"> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="upper A"> …