[1] Colojoara I., Foiaş C: 
Generalized spectral operators. Gordon and Breach, Science Publishers, New York, 1968. 
MR 0394282[2] Dunford N., Schwartz J.: 
Linear operators. Part III: Spectral operators. Wiley-Interscience, New York, 1971. 
MR 1009164 | 
Zbl 0243.47001[3] Foiaş  С: 
Une application des distributions vectorielles à la théorie spectrale. Bull. Sci. Math. (2), 84 (1960), 147-158. 
MR 0123193[5] Hörmander L.: 
Linear partial differential operators. Springer-Verlag, 1963. 
MR 0404822[7] Pták V., Vrbová P.: 
On the spectral function of a normal operator. Czech. Math. J. 23 (98), (1973), 615-616. 
MR 0336421[9] Vrbová P.: 
The structure of maximal spectral spaces of generalized scalar operators. Czech. Math. J. 23 (98), (1973), 493-496. 
MR 0320804