MLA

Miłosz, Czesław, 1911-2004. Wańkowicz, Melchior. Box 67, folder 920. 1951-1961, undated. https://collections.library.yale.edu/catalog/10081392.

APA, 6th edition

Miłosz, Czesław, 1911-2004. (["Box 67, folder 920"])(1951-1961, undated)[Wańkowicz, Melchior]. https://collections.library.yale.edu/catalog/10081392.