APA (7th ed.) Citation

Athletic Institute & Guennel, G. K. (1950). How to improve your soccer. [publisher not identified].

Chicago Style (17th ed.) Citation

Athletic Institute and Gottfried Kurt Guennel. How to Improve Your Soccer. Chicago: [publisher not identified], 1950.

MLA (9th ed.) Citation

Athletic Institute and Gottfried Kurt Guennel. How to Improve Your Soccer. [publisher not identified], 1950.