APA
Helmberg G., Koiter W. & Lauwerier H. (1969). Introduction to spectral theory in Hilbert space. Amsterdam: North Holland Personal Library.
Chicago
Helmberg Gilbert, Koiter W and Lauwerier H. 1969. Introduction to spectral theory in Hilbert space. Amsterdam: North Holland Personal Library.
Harvard
Helmberg G., Koiter W. and Lauwerier H. (1969). Introduction to spectral theory in Hilbert space. Amsterdam: North Holland Personal Library.
MLA
Helmberg Gilbert, Koiter W and Lauwerier H. Introduction to spectral theory in Hilbert space. Amsterdam: North Holland Personal Library. 1969.