Citazione APA

Hawking, L., & Hawking, S. W. G. (2007). George's secret key to the universe. Doubleday.

Stile di citazione Chicago

Hawking, Lucy, e Stephen W. Galfard Hawking. George's Secret Key to the Universe. London: Doubleday, 2007.

Citazione MLA

Hawking, Lucy, e Stephen W. Galfard Hawking. George's Secret Key to the Universe. Doubleday, 2007.