MLA

Kissinger, Henry, 1923-2023. Sommer, Theodor. Box 55, folder 23. 1960-1961. https://collections.library.yale.edu/catalog/11783451.

APA, 6th edition

Kissinger, Henry, 1923-2023. (["Box 55, folder 23"])(1960-1961)[Sommer, Theodor]. https://collections.library.yale.edu/catalog/11783451.