MLA

Congdon, and Charles R Keeton. Principles of Gravitational Lensing. Springer International Publishing, 2018.

APA

Congdon, C., & Keeton, C. R. (2018). Principles of Gravitational Lensing. Springer International Publishing.

Chicago

Congdon, and Charles R Keeton. Principles of Gravitational Lensing. : Springer International Publishing, 2018.