MLA

Gabo, Naum, 1890-1977. Richter-Gabo, Elizabeth. Box 33. 1939-1980. https://collections.library.yale.edu/catalog/17170362.

APA, 6th edition

Gabo, Naum, 1890-1977. (["Box 33"])(1939-1980)[Richter-Gabo, Elizabeth]. https://collections.library.yale.edu/catalog/17170362.