MLA

Miłosz, Czesław, 1911-2004. Ginsberg, Allen. Box 138, folder 2180. undated. https://collections.library.yale.edu/catalog/10050469.

APA, 6th edition

Miłosz, Czesław, 1911-2004. (["Box 138, folder 2180"])(undated)[Ginsberg, Allen]. https://collections.library.yale.edu/catalog/10050469.