MLA

Sartre, Jean-Paul, 1905-1980. Interview 21. Box 1, folder 20. 1972 Jan 21. https://collections.library.yale.edu/catalog/16538174.

APA, 6th edition

Sartre, Jean-Paul, 1905-1980. (["Box 1, folder 20"])(1972 Jan 21)[Interview 21]. https://collections.library.yale.edu/catalog/16538174.