On the deficiency indices of powers of formally symmetric differential expressions. With three Addenda by T. T. Read, R. M. Kauffman and Anton Zettl. (English) Zbl 0315.34010

Spectral Theor. differ. Equat., Proc. Symp. Dundee 1974, Lect. Notes Math. 448, 167-181 (1975).


34A30 Linear ordinary differential equations and systems
47E05 General theory of ordinary differential operators