Nonself-adjoint differential operators in direct sum spaces (Q1209553)

In Rocky Mt. J. Math. 16, 497-516 (1986; Zbl 0624.34020), \textit{W. N. Everitt} and \textit{A. Zettl} considered the problem of characterizing all the self-adjoint operators which can be generated by formally symmetric Sturm-Liouville differential expressions \(M_ p\) \((p= 1,2)\) defined on two intervals \(I_ p\) \((p= 1,2)\) with boundary conditions at the endpoints. The aim of the paper under review is to extend the results of loc. cit. to the case where the differential expressions \(M_ p\) are arbitrary and there is a finite number of intervals \(I_ p\), \(p= 1,2,\dots, N\).