MLA

Chopin, Henri, 1922-2008. La poetique = savoir exact. Box 25. undated. https://collections.library.yale.edu/catalog/17289285.

APA, 6th edition

Chopin, Henri, 1922-2008. (["Box 25"])(undated)[La poetique = savoir exact]. https://collections.library.yale.edu/catalog/17289285.