MLA

Kissinger, Henry, 1923-2023. Szilard, Leo. Box 58, folder 5. 1961. https://collections.library.yale.edu/catalog/11783502.

APA, 6th edition

Kissinger, Henry, 1923-2023. (["Box 58, folder 5"])(1961)[Szilard, Leo]. https://collections.library.yale.edu/catalog/11783502.