APA (7th ed.) Citation

Gent, I. P., & Walsh, T. (1993). Easy problems are sometimes hard.

Chicago Style (17th ed.) Citation

Gent, Ian P., and Toby Walsh. Easy Problems Are Sometimes Hard. Edinburgh, 1993.

MLA (9th ed.) Citation

Gent, Ian P., and Toby Walsh. Easy Problems Are Sometimes Hard. 1993.

Warning: These citations may not always be 100% accurate.