MLA

Wolff, Kurt, 1887-1963. Einstein, Carl. Box 2, folder 52. [1910]-23. https://collections.library.yale.edu/catalog/2021307.

APA, 6th edition

Wolff, Kurt, 1887-1963. (["Box 2, folder 52"])([1910]-23)[Einstein, Carl]. https://collections.library.yale.edu/catalog/2021307.