MLA

Schwartz, Delmore, 1913-1966. "Exercise". Box 3, folder 164. 1914-circa 1945. https://collections.library.yale.edu/catalog/17405218.

APA, 6th edition

Schwartz, Delmore, 1913-1966. (["Box 3, folder 164"])(1914-circa 1945)["Exercise"]. https://collections.library.yale.edu/catalog/17405218.