MLA

Kaufman, Boris (1906-1980). Kepes, Juliet. Box 13, folder 228. 1976-79, n.d.. https://collections.library.yale.edu/catalog/16591743.

APA, 6th edition

Kaufman, Boris (1906-1980). (["Box 13, folder 228"])(1976-79, n.d.)[Kepes, Juliet]. https://collections.library.yale.edu/catalog/16591743.