MLA

Stettheimer, Florine, 1871-1944. Duchamp, Marcel. Box 1, folder 19-20. 1917-46, n.d.. https://collections.library.yale.edu/catalog/17054786.

APA, 6th edition

Stettheimer, Florine, 1871-1944. (["Box 1, folder 19-20"])(1917-46, n.d.)[Duchamp, Marcel]. https://collections.library.yale.edu/catalog/17054786.