MLA

Matthiessen, F. O. (Francis Otto), 1902-1950. Willkie, Wendell. Box 4. 1942 November 6. https://collections.library.yale.edu/catalog/32240053.

APA, 6th edition

Matthiessen, F. O. (Francis Otto), 1902-1950. (["Box 4"])(1942 November 6)[Willkie, Wendell]. https://collections.library.yale.edu/catalog/32240053.