APA (7th ed.) Citation

Guy, R. K. (1981). Unsolved problems in intuitive mathematics. Springer-Verlag.

Chicago Style (17th ed.) Citation

Guy, Richard K. Unsolved Problems in Intuitive Mathematics. New York, N.Y.: Springer-Verlag, 1981.

MLA (9th ed.) Citation

Guy, Richard K. Unsolved Problems in Intuitive Mathematics. Springer-Verlag, 1981.