1. ALEXANDROFF, P. und HOPF, H.: Topologie I, Berlin, Springer 1935
2. APOSTOL, C.: Spectral Decomposition and Functional calculus, Rev. Roum. Math. Pures Appl. 13, 1481?1528 (1968)
3. APOSTOL, C.: Remarks on the Perturbation and a Topology for Operators. J. Functional Anal. 2, 395?408 (1968)
4. COLOJOAR?, I. and FOJA?, C.: Theory of Generalized Spectral Operators, New York, Gordon and Breach 1968.
5. COLOJOAR?, I. and FOJA?, C.: Quasi-nilpotent Equivalence of nor Necessarily Commuting Operators, J. Math. Mech. 15, 521?540 (1965)