MLA

Steinberg, Saul, 1914-1999. Hofer, Evelyn. Box 232, folder 3977. 1967-1973, undated. https://collections.library.yale.edu/catalog/33452452.

APA, 6th edition

Steinberg, Saul, 1914-1999. (["Box 232, folder 3977"])(1967-1973, undated)[Hofer, Evelyn]. https://collections.library.yale.edu/catalog/33452452.