MLA

Stieglitz, Alfred, 1864-1946. Marcel Duchamp. Box 124, folder 2471-2472. [1923]. https://collections.library.yale.edu/catalog/16627610.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 124, folder 2471-2472"])([1923])[Marcel Duchamp]. https://collections.library.yale.edu/catalog/16627610.