ABSTRACT
Let H $ \mathcal H $ https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203709733/a3b86244-1034-43cb-9a0d-166f5a5cedfd/content/inline-math3_1.tif"/> be a Hilbert space and let L ( H ) $ \mathcal L (\mathcal H ) $ https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203709733/a3b86244-1034-43cb-9a0d-166f5a5cedfd/content/inline-math3_2.tif"/> denote the collection of all bounded linear operators on H $ \mathcal H $ https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203709733/a3b86244-1034-43cb-9a0d-166f5a5cedfd/content/inline-math3_3.tif"/> . An operator T ∈ L ( H ) $ T\in \mathcal L (\mathcal H ) $ https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203709733/a3b86244-1034-43cb-9a0d-166f5a5cedfd/content/inline-math3_4.tif"/> is called an isometry if T f , T g H = f , g H $$ \left(Tf,Tg\right)_{ \mathcal H }=\left(f,g\right)_{ \mathcal H } $$ https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203709733/a3b86244-1034-43cb-9a0d-166f5a5cedfd/content/um474.tif"/>
