MLA

Brodsky, Joseph, 1940-1996. Vegin, Petr. Box 15, folder 412. 1980-1989, undated. https://collections.library.yale.edu/catalog/32404001.

APA, 6th edition

Brodsky, Joseph, 1940-1996. (["Box 15, folder 412"])(1980-1989, undated)[Vegin, Petr]. https://collections.library.yale.edu/catalog/32404001.