Perturbation theorems for Hermitian elements in Banach algebras
Rajendra Bhatia, Driss Drissi · Studia Mathematica · 1999
Two well-known theorems for Hermitian elements in C*-algebras are extended to Banach algebras. The first concerns the solution of the equation ax - xb = y, and the second gives sharp bounds for the distance between spectra of a and b when a, b are Hermiti