Derkach V. Malamud M., “Generalized Resolvents and the Boundary-Value-Problems for Hermitian Operators with Gaps”, J. Funct. Anal., 95:1 (1991), 1–95
È. L. Pekarev, “Angular operators of nondegenerate subspaces”, Funct. Anal. Appl., 25:1 (1991), 72–73
Derkach V. Malamud M., “On the Weil Functions and Hermitian Operators with Lacunas”, 293, no. 5, 1987, 1041–1046
G. Nenciu, “Theory of the self-adjoint extensions of symmetric operators with a spectral gap”, Funct. Anal. Appl., 19:1 (1985), 69–70
Yu. M. Arlinskii, È. R. Tsekanovskii, “Non-self-adjoint contractive extensions of a Hermitian contraction and theorems of Krein”, Russian Math. Surveys, 37:1 (1982), 151–152
M. M. Gekhtman, “Existence of surface conditions for nonclassical self-adjoint extensions of the Laplace operator”, Funct. Anal. Appl., 16:1 (1982), 49–51
È. R. Tsekanovskii, “Friedrichs and Krein extensions of positive operators and holomorphic contraction semigroups”, Funct. Anal. Appl., 15:4 (1981), 308–309
È. R. Tsekanovskii, “Non-self-adjoint accretive extensions of positive operators and theorems of Friedrichs–Krein–Phillips”, Funct. Anal. Appl., 14:2 (1980), 156–157
È. L. Pekarev, “Convolutions onto an operator domain”, Funct. Anal. Appl., 12:3 (1978), 230–231
È. R. Tsekanovskii, Yu. L. Shmul'yan, “The theory of bi-extensions of operators on rigged Hilbert spaces. Unbounded operator colligations and characteristic functions”, Russian Math. Surveys, 32:5 (1977), 73–131
M. L. Gorbachuk, “Self-adjoint boundary problems for a second-order differential equation with unbounded operator coefficient”, Funct. Anal. Appl., 5:1 (1971), 9–18