MLA

Kissinger, Henry, 1923-2023. Gumbel, Karl. Box 26, folder 12. 1964-1966. https://collections.library.yale.edu/catalog/11782794.

APA, 6th edition

Kissinger, Henry, 1923-2023. (["Box 26, folder 12"])(1964-1966)[Gumbel, Karl]. https://collections.library.yale.edu/catalog/11782794.