MLA

Kagan, Paul, 1943-1993. Correspondence. Box 1, folder 3. 1944. https://collections.library.yale.edu/catalog/16312592.

APA, 6th edition

Kagan, Paul, 1943-1993. (["Box 1, folder 3"])(1944)[Correspondence]. https://collections.library.yale.edu/catalog/16312592.