MLA

Kissinger, Henry, 1923-2023. Gell-Mann, Murray. Box 24, folder 12. Undated, circa 1968. https://collections.library.yale.edu/catalog/11782751.

APA, 6th edition

Kissinger, Henry, 1923-2023. (["Box 24, folder 12"])(Undated, circa 1968)[Gell-Mann, Murray]. https://collections.library.yale.edu/catalog/11782751.