MLA

Herbert, Zbigniew, 1924-1998. Herling-Grudzinski, Gustaw. Box 1, folder 20. 1987-88, n.d.. https://collections.library.yale.edu/catalog/16591594.

APA, 6th edition

Herbert, Zbigniew, 1924-1998. (["Box 1, folder 20"])(1987-88, n.d.)[Herling-Grudzinski, Gustaw]. https://collections.library.yale.edu/catalog/16591594.