MLA

Steinberg, Saul, 1914-1999. Postcards. Box 190 | Box 191 | Box 192 | Box 193 | Box 194 | Box 195 | Box 196 | Box 197 | Box 198 | Box 199. undated. https://collections.library.yale.edu/catalog/2016622.

APA, 6th edition

Steinberg, Saul, 1914-1999. (["Box 190 | Box 191 | Box 192 | Box 193 | Box 194 | Box 195 | Box 196 | Box 197 | Box 198 | Box 199"])(undated)[Postcards]. https://collections.library.yale.edu/catalog/2016622.