MLA

Kagan, Paul, 1943-1993. Caspar Compound. Box 3, folder 99. 1972 July. https://collections.library.yale.edu/catalog/10191498.

APA, 6th edition

Kagan, Paul, 1943-1993. (["Box 3, folder 99"])(1972 July)[Caspar Compound]. https://collections.library.yale.edu/catalog/10191498.