MLA

Steinberg, Saul, 1914-1999. Untitled [Yellow business envelope with 22 cent United States Postal Service stamp]. Box 75, folder 1434. 1987. https://collections.library.yale.edu/catalog/16855715.

APA, 6th edition

Steinberg, Saul, 1914-1999. (["Box 75, folder 1434"])(1987)[Untitled [Yellow business envelope with 22 cent United States Postal Service stamp]]. https://collections.library.yale.edu/catalog/16855715.