Neerven, Jan van
The adjoint of a semigroup of linear operators
Springer-Verlag, 1992
 Buku Teks
Dunford, Nelson
Linear operators part 2: spectral theory, self adjoint operators in Hilbert space
John Wiley & Sons, 1963
 Buku Teks
Schmüdgen, Konrad
Unbounded self-adjoint operators on Hilbert space
Springer, 2012
 eBooks
Dowson, H.R.
Spectral theory of linear operators
Academic Press, 1978
 Buku Teks
Lanczos, Cornelius, 1893-
Linear differential operators
Society for Industrial and Applied Mathematics, 1996
 eBooks