Rössler, Ulrich (2013-06-29). Solid State Theory: An Introduction. Springer Science+Business Media. p. 203. ISBN 978-3-662-09940-7. 978-3-662-09940-7 ↩
Economou, Eleftherios N. (2006-08-02). Green's Functions in Quantum Physics. Springer Science+Business Media. p. 276. ISBN 978-3-540-28841-1. 978-3-540-28841-1 ↩