MLA

Serge, Victor, 1890-1947. Guérin, Daniel. Box 1, folder 37. 1945-46. https://collections.library.yale.edu/catalog/17455284.

APA, 6th edition

Serge, Victor, 1890-1947. (["Box 1, folder 37"])(1945-46)[Guérin, Daniel]. https://collections.library.yale.edu/catalog/17455284.