MLA

Berberova, N. (Nina), 1901-1993. Yakobson, Helen. Box 22, folder 638. 1964-80, n.d.. https://collections.library.yale.edu/catalog/16688046.

APA, 6th edition

Berberova, N. (Nina), 1901-1993. (["Box 22, folder 638"])(1964-80, n.d.)[Yakobson, Helen]. https://collections.library.yale.edu/catalog/16688046.