MLA

Wilson, Elena, 1906-1979. Updike, John. Box 6, folder 265. 1976 Feb 27. https://collections.library.yale.edu/catalog/17197607.

APA, 6th edition

Wilson, Elena, 1906-1979. (["Box 6, folder 265"])(1976 Feb 27)[Updike, John]. https://collections.library.yale.edu/catalog/17197607.