MLA

Serge, Victor, 1890-1947. Breton, André. Box 1, folder 9. 1940-41. https://collections.library.yale.edu/catalog/16495422.

APA, 6th edition

Serge, Victor, 1890-1947. (["Box 1, folder 9"])(1940-41)[Breton, André]. https://collections.library.yale.edu/catalog/16495422.