MLA

Van Vechten, Carl, 1880-1964. Prokosch, Frederic. Box 371, folder 5291. 1952 April 1. https://collections.library.yale.edu/catalog/10001341.

APA, 6th edition

Van Vechten, Carl, 1880-1964. (["Box 371, folder 5291"])(1952 April 1)[Prokosch, Frederic]. https://collections.library.yale.edu/catalog/10001341.