ABSTRACT
Denote https://www.w3.org/1998/Math/MathML"> ( + ) ( ℋ ) : = { R ∈ ( ℋ ) : R i s i n v e r t i b l e a n d o f t h e f o r m u n i t a r y operator p l u s c ompact operator } . ℳ https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203738139/6b6b2f71-5425-486e-94f7-969020be3717/content/math328.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/>
