APA (7th ed.) Citation

Calderón, M. (1999). Avoiding character collisions in games. [publisher not identified].

Chicago Style (17th ed.) Citation

Calderón, Manuel. Avoiding Character Collisions in Games. [Place of publication not identified]: [publisher not identified], 1999.

MLA (9th ed.) Citation

Calderón, Manuel. Avoiding Character Collisions in Games. [publisher not identified], 1999.