1. Atkinson, F.V.: Normal solvability of linear equations in normalized spaces. Matem. Sbornik 28, 3–14 (1951) (In Russian).
2. Dieudonné, J.: Sur les homomorphismes d’espaces normés. Bull. Sci. Math. 67, 72–84 (1943).
3. Dieudonné, J.: The index of operators in Banach spaces. Integral Eq. and Operator Theory 8, 580–589 (1985).
4. Heuser, H.: Funktionalanalysis, 4. Aufl. Teubner-Verlag, Stuttgart 2006.
5. Jörgens, K.: Lineare Integraloperatoren. Teubner-Verlag, Stuttgart 1970.