MLA

Serge, Victor, 1890-1947. Laurat, Lucien. Box 1, folder 45. 1939-47. https://collections.library.yale.edu/catalog/16495433.

APA, 6th edition

Serge, Victor, 1890-1947. (["Box 1, folder 45"])(1939-47)[Laurat, Lucien]. https://collections.library.yale.edu/catalog/16495433.