MLA

Dreier, Katherine S. (Katherine Sophie), 1877-1952. "An Open Letter" [on Cubism], typescript carbon. Box 42, folder 1249. [1925]. https://collections.library.yale.edu/catalog/16694438.

APA, 6th edition

Dreier, Katherine S. (Katherine Sophie), 1877-1952. (["Box 42, folder 1249"])([1925])["An Open Letter" [on Cubism], typescript carbon]. https://collections.library.yale.edu/catalog/16694438.