MLA

Kissinger, Henry, 1923-2023. Ritter, Karl-Heinz. Box 362, folder 1. 1971. https://collections.library.yale.edu/catalog/11775422.

APA, 6th edition

Kissinger, Henry, 1923-2023. (["Box 362, folder 1"])(1971)[Ritter, Karl-Heinz]. https://collections.library.yale.edu/catalog/11775422.