MLA

Van Thal, Herbert, 1904-1983. Mortimer, Raymond. Box 1, folder 86. 1957 May 7. https://collections.library.yale.edu/catalog/16545990.

APA, 6th edition

Van Thal, Herbert, 1904-1983. (["Box 1, folder 86"])(1957 May 7)[Mortimer, Raymond]. https://collections.library.yale.edu/catalog/16545990.