MLA

Cunard, Nancy, 1896-1965. Tzara, Tristan. Box 1, folder 31. [n.y.] Jan 8. https://collections.library.yale.edu/catalog/16538148.

APA, 6th edition

Cunard, Nancy, 1896-1965. (["Box 1, folder 31"])([n.y.] Jan 8)[Tzara, Tristan]. https://collections.library.yale.edu/catalog/16538148.