FILOMAT, cilt.28, sa.5, ss.917-923, 2014 (SCI-Expanded)
In the paper of W.N. Everitt and A. Zettl [26] in scalar case, all selfadjoint extensions of the minimal operator generated by Lagrange-symmetric any order quasi-differential expression with equal deficiency indexes in terms of boundary conditions are described by Glazman-Krein-Naimark method for regular and singular cases in the direct sum of corresponding Hilbert spaces of functions. In this work, by using the method of Calkin-Gorbachuk theory all normal extensions of the minimal operator generated by fixed order linear singular multipoint differential expression l = (l(-), l(1), ... , l(n), l(+)), l(-/+) = d/dt + A(-/+), l(k) = d/dt + A(k) where the coefficients A(-/+), A(k) are selfadjoint operator in separable Hilbert spaces H--/+, H-k, k = 1, ... , n, n is an element of N respectively, are researched in the direct sum of Hilbert spaces of vector-functions