Παραπομπή APA

Hawking,Stephen, & Penrose,Roger. (1999). The Nature of Space and Time. OUP.

Παραπομπή Chicago Style

Hawking,Stephen, και Penrose,Roger. The Nature of Space and Time. Delhi: OUP, 1999.

Παραπομπή MLA

Hawking,Stephen, και Penrose,Roger. The Nature of Space and Time. OUP, 1999.