MLA

Steinberg, Saul, 1914-1999. "B" General. Box 4, folder 55-65 | Box 5, folder 66-67. 1945-1998, undated. https://collections.library.yale.edu/catalog/2017291.

APA, 6th edition

Steinberg, Saul, 1914-1999. (["Box 4, folder 55-65 | Box 5, folder 66-67"])(1945-1998, undated)["B" General]. https://collections.library.yale.edu/catalog/2017291.