MLA

Berberova, N. (Nina), 1901-1993. Smithsonian. Box 54, folder 1257. n.d.. https://collections.library.yale.edu/catalog/10454519.

APA, 6th edition

Berberova, N. (Nina), 1901-1993. (["Box 54, folder 1257"])(n.d.)[Smithsonian]. https://collections.library.yale.edu/catalog/10454519.