Hall, Graham (2004). Symmetries and Curvature Structure in General Relativity (World Scientific Lecture Notes in Physics). Singapore: World Scientific Pub. Co. ISBN981-02-1051-5.
Stephani, Hans; Kramer, Dietrich; MacCallum, Malcolm; Hoenselaers, Cornelius & Herlt, Eduard (2003). Exact Solutions of Einstein's Field Equations. Cambridge: Cambridge University Press. ISBN0-521-46136-7.{{cite book}}: نگهداری یادکرد:نامهای متعدد:فهرست نویسندگان (link)See Section 24.5
Sippel, R.; & Gönner, H. (1986). "Symmetry classes of pp waves". Gen. Rel. Grav. 12: 1129–1243.{{cite journal}}: نگهداری یادکرد:نامهای متعدد:فهرست نویسندگان (link)
Penrose, Roger (1976). "Any spacetime has a plane wave as a limit". Differential Geometry and Relativity. pp. 271–275.
