MLA

Brodsky, Joseph, 1940-1996. Introduction of Czesław Miłosz and Paul Muldoon at the Library of Congress. Box 123, folder 2788. 1991 or 1992. https://collections.library.yale.edu/catalog/17465200.

APA, 6th edition

Brodsky, Joseph, 1940-1996. (["Box 123, folder 2788"])(1991 or 1992)[Introduction of Czesław Miłosz and Paul Muldoon at the Library of Congress]. https://collections.library.yale.edu/catalog/17465200.