MLA

Stieglitz, Alfred, 1864-1946. "Gertrude Stein," holograph. Box 99, folder 2013. 1912 [?]. https://collections.library.yale.edu/catalog/32258194.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 99, folder 2013"])(1912 [?])["Gertrude Stein," holograph]. https://collections.library.yale.edu/catalog/32258194.