Measures of Noncompactness and Upper Semi-Fredholm Perturbation Theorems
Measures of Noncompactness and Upper Semi-Fredholm Perturbation Theorems
We introduce the concept of a perturbation function, which allows us to give a general approach to the question of obtaining perturbation theorems for upper semi-Fredholm operators.Also, we show that the usual measures of noncompactness of continuous linear operators, as well as other related quantities, are perturbation functions.