APA (7th ed.) Citation

Wehrli, R. (1968). Open-ended problem solving in design. [publisher not identified].

Chicago Style (17th ed.) Citation

Wehrli, Robert. Open-ended Problem Solving in Design. [Place of publication not identified]: [publisher not identified], 1968.

MLA (9th ed.) Citation

Wehrli, Robert. Open-ended Problem Solving in Design. [publisher not identified], 1968.