MLA

[Letters : Multiple Correspondents, 1966 to Saul Steinberg]. 0AD. https://collections.library.yale.edu/catalog/10034264.

APA, 6th edition

[Letters : multiple correspondents, 1966 to Saul Steinberg]. (0 C.E.). [Autographs, Business records, correspondence (AAT), drawings (AAT), Greeting cards, manuscripts (AAT), Photographic prints.--aat, photographs (AAT), postcards (AAT), Receipts, Typescripts]. https://collections.library.yale.edu/catalog/10034264.