MLA

Kagan, Paul, 1943-1993. International Ideal City. Box 3, folder 93. 1972 July. https://collections.library.yale.edu/catalog/10191445.

APA, 6th edition

Kagan, Paul, 1943-1993. (["Box 3, folder 93"])(1972 July)[International Ideal City]. https://collections.library.yale.edu/catalog/10191445.