MLA

Filippov, Boris, 1905-1991. Letters. Box 8, folder 232-244. 1964-65. https://collections.library.yale.edu/catalog/16537956.

APA, 6th edition

Filippov, Boris, 1905-1991. (["Box 8, folder 232-244"])(1964-65)[Letters]. https://collections.library.yale.edu/catalog/16537956.