MLA

Stein, Leo, 1872-1947. Coubine, Otakar. Box 1, folder 3-4. 1926-47. https://collections.library.yale.edu/catalog/17155337.

APA, 6th edition

Stein, Leo, 1872-1947. (["Box 1, folder 3-4"])(1926-47)[Coubine, Otakar]. https://collections.library.yale.edu/catalog/17155337.