APA (7th ed.) Citation

Gibbons, J., Hutton, G., & Altenkirch, T. (2001). When is a function a fold or an unfold? Elsevier Science.

Chicago Style (17th ed.) Citation

Gibbons, Jeremy, Graham Hutton, and Thorsten Altenkirch. When Is a Function a Fold or an Unfold? Elsevier Science, 2001.

MLA (9th ed.) Citation

Gibbons, Jeremy, et al. When Is a Function a Fold or an Unfold? Elsevier Science, 2001.