MLA

Serge, Victor, 1890-1947. "Le Guépéou à l'oeuvre à Mexico," typescript carbon. Box 3, folder 155. n.d.. https://collections.library.yale.edu/catalog/16495450.

APA, 6th edition

Serge, Victor, 1890-1947. (["Box 3, folder 155"])(n.d.)["Le Guépéou à l'oeuvre à Mexico," typescript carbon]. https://collections.library.yale.edu/catalog/16495450.